The Forensic Teacher Magazine: Let’s first talk about firearms in general, and let’s see from there. Why firearms? What is it about firearms that fascinated you that you wanted to become an expert in them?

Dr. Peter Diaczuk: It’s really how different they all are from one another. Many have been invented by different people, or by the same person like John Browning, his designs have evolved over time. And then also from not only the mechanical aspect, but an appreciation of just how much they were able to do in a time when computers were not around to assist them in such designs. Again, John Browning was designing firearms in the late 1890s and some of them have almost no change or very little changes from a safety standpoint; they’re still around today. In fact his .45 – the model of 1911 celebrated its centennial just a few years ago.

Anyway, from a mechanical standpoint, there are a couple of different things that a firearm has to go through: a lot of high energy situations and a lot of trauma when they’re fired. And then, the transformation of the chemical energy of the propellant to the kinetic energy of the bullet, which goes hand in hand with the mechanical design. The strength, the metallurgy, and such; these things have always fascinated me. So, consequently, when I see a firearm I am interested in knowing how it works, and how it manages to cycle ammunition through it. With my college training and education in forensic science, there’s an application there to look at firearms and ammunition, fired ammunition from the sense of what firearm discharged a bullet or discharged a spent case, or how close a firearm’s muzzle was to a target. All these things just sort of tied in for me when I was younger. When I was in high school, I was interested in chemistry and mechanical engineering but I was leaning more towards chemistry and I was going to pursue a degree in chemical engineering.

FT: Good.

PD: At this time my senior year in high school I took out a book from the high school library entitled Science against Crime, and on the cover was a fellow in a lab coat holding a double barrel shotgun, either about to fire it or just having fired it. And I thought, ‘holy smokes, here’s firearms and science put together in the same photograph,’ and reading through the book I saw that forensic science was potentially where I could put two things that I like a lot, science and firearms, together.

FT: Nice.

PD: That was what made me decide to go to John Jay College, when I graduated high school.

FT: Cool. So, you had the interest and you knew what was out there, but how did you get into the field as a vocation?

PD: I have to give all thanks to my professor, Dr. Peter De Forest. He was instrumental not only in my education because he was my professor of criminalistics at John Jay College, but then he also allowed me to assist him on casework, and that’s where I got my feet wet because otherwise I might not be doing this.

FT: That’s nice. It’s always satisfying to have someone who gives you a hand up. What about firearms research going on today? I read something about research going on concerning firearms and tool marks for forensics. What can you tell us about that? In other words, what are forensic tool mark examiners and firearms examiners becoming aware of that hasn’t hit TV yet?

PD: Well, I don’t watch that much TV, but I will say that a combination of the NAS [National Academy of Science] report of a few years ago, and increasing challenges in court about the exact wording of testimony about how a certain piece of ammunition may have originated from a certain firearm has propagated an increasing interest in applying statistics to the conclusions that are made by firearm examiners. Or, it’s not statistics and also just the certainty of the statements and how those statements should be worded properly. So, as a result, what’s really neat, is that I have the distinct honor, despite the fact that Dr. De Forest has recently retired from John Jay College, to work with some folks there, Dr. Nick Petraco, Dr. Thomas Kubic, professor Petraco, Dr. Nick’s father, who are involved in research collectively under the roof of John Jay College.

FT: Nice.

PD: Using computers, and by no means am I suggesting they’ll replace an individual doing a comparison, but the computers are looking at it purely objectively, and there can sometimes be an ineffective argument

, but nevertheless, there could be an argument that an examiner is biased in some way, or is making a subjective conclusion about whether or not two pieces of ammunition came from the same source. The computer program is currently being used to validate the human decision-making process.

FT: Gotcha.

PD: So, Dr. Petraco and his group of firearm and tool mark researchers are working with comparison microscopy, confocal microscopy, statistics, and a few programs that he wrote in order to have the computer digest this information. The computer is assessing whether or not two pieces of ammunition came from the same firearm or different firearms, and once again the computer has no agenda. It can’t be biased by reading a statement or being told something from an investigator or reading something in a report, so the computer is looking at the surface topography and deciding whether or not the two samples are the same. Concurrent with that, we’re using the more traditional method of optical microscopy with a comparison microscope to see if an examiner is making the same decision, so it is a neat validation, if you will. Comparison microscopy has been used for about a century, plus or minus, depending on what you want to call the beginning. Regardless, it has been around for a century yet it was questioned in the 2009 report, and again by some attorneys. Unfortunately those attorneys don’t have experience using the comparison microscope yet they’re complaining anyway.

FT: You know, some attorneys will always complain.

PD: I’m excited about this work because it could set the record straight and answer the critics’ challenges to whether or not the comparison microscopy is, in fact, valid or not.

FT: Okay, good. I think your decision not to watch a lot of TV is probably a very smart one given the lot of the crap that is on today. But one thing I am curious about, from a real life examiner’s point is how much, or do you get a feeling or do you have any experience about—do the crooks on the street, do guys who are normally carrying guns, and using them and doing all sorts of senseless acts of violence with it, do they actually know about guns or are they just think they know about guns from watching movies and TV? I mean like the guys who hold the gun sideways with one hand when they are about to fire. Do they not realize that you can trace a bullet back to a certain gun?

PD: I am going to be a little speculative here. First of all, I am delighted if folks who should not be using guns are not doing it correctly. That’s great. Then, it is very likely that they wouldn’t hurt anyone, or ideally they would just hurt themselves (laughs).

FT: Yeah.

PD: I believe there has been a lot of information on TV over the past decade, and it even goes before that, shows like Quincy. Where certain things were shown on TV where folks who are using guns in an illegal fashion can learn something if that’s what you’re asking me, that’s unfortunate for other folks who are trying to use the science against crime.

FT: Yeah.

PD: I mean as long as we are one step ahead of the bad guys we hope for the best and hope to be able to resolve the issue. If the folks involved in forensic science can not only suggest information that ties a suspect to a victim, but also suggest information that eliminates people of interest from being involved in some criminal activity, it works both ways.

FT: Hey speaking of test shots, I know a lot of TV is inaccurate and we’ve got to squeeze all the stuff in before the commercial, but cops will recover a gun and they will bring it back, test fire it into a tank of water, pull out the bullet put it on the comparison scope and within ten seconds say that’s it. How long does it really take?

PD: It’s a good question, the firing in the water is accurate and the comparison microscope is accurate, but it kind of depends on the firearm itself. Some are very difficult to locate marks that are sufficient to make a conclusion of common origin, and in other ones it is much easier. A lot depends on the rifling characteristics, on the wear of the gun, and who made the gun. The less expensive ones may use different manufacturing techniques that don’t leave profound marks on the ammunition.

Also the storage and handling of the gun once it left the factory, if it is in a damp basement, in the damp trunk of a car, and what had happened with the firearm from when it was fired in a criminal act, to when it was recovered, if that is a long time span, and if the firearm has been kept in a poor condition then we are dealing with situation where the microscopy takes longer. So the microscopy could take as little as a half hour or it could take several hours or depending upon the sample it may be unsuitable for comparison.

FT: Wow.

PD: You want to assure yourself, depending on what your conclusion is as well. In addition it is important to know whether, this is an investigative lead where the level of proof or certainty is lower, or is it for the adjudicate stage where the level of certainty has to be considerably higher. For an investigative lead sometimes a lesser amount of time on the microscope is satisfactory for an initial assessment. Making these decisions is important because the investigators have to be interviewing people and making decisions quickly based on some useful information from the lab, whereas, in an adjudicative sense everything has to withstand additional scrutiny and possibly be challenged by the opposing expert.

FT: I see...

PD: A lot more is at stake in the adjudicative stage in an investigation. You may have to spend considerably more time looking at all aspects of whether or not two pieces of ammunition came from the same firearm and that may not even be the only question at hand. Admittedly, the traditional comparison microscopy and historic firearm examiner work is whether or not a piece of ammunition came from the same firearm, different firearms, or specific firearm if one is not recovered, There may be occasions, however, when this may not be in dispute, when it’s not the question at hand, maybe one person fired a couple of shots and doesn’t deny firing those shots, but instead has a specific secondary story behind that involving distance or whether a door is opened or closed or a window was opened or closed and someone unfortunately was in the bullet’s path. There can be a multitude of different circumstances for example those instances when the person says yes, I fired those bullets, that was definitely me. There were no other guns around. But I fired because my life was threatened or a similar scenario where sometimes muzzle to target distances come into play.

  Other times maybe bullet damage comes into play where you have to assess what the bullet went through in its journey before it came to rest and also trace evidence on the bullet. Sometimes, there’s a bullet that picks up paint, fibers from a garment, concrete debris from a ricochet.

FT: Right.

PD: In such cases where the bullet is telling a story, it’s up to the forensic scientist to interpret that story.

FT: Ahh. Okay, now speaking about doing ID’s on bullets, I guess your field uses IBIS?

PD: Well, I don’t use IBIS because. that’s restricted to law enforcement and I am in the private sector, and I teach at the college. IBIS or NIBIN, those are the firearm community’s version of what the DNA people use as CODIS and what the fingerprint people use as AFIS, so it is a system where data is inputed from fired ammunition. Of course that data has to be good. If the inputted data is poor, the results will be poor as well. The computer with its speed and ability to go through a lot of user information will, in a short bit of time, suggest several potential hits.

FT: Okay.

PD: Then, just like it is in the other two disciplines, if the computer suggests possible candidates it’s up to an examiner to then physically make the comparison, but it certainly cuts down on a lot of labor intensive work before a conclusion is made. So it is a great time saving element and it’s able to connect evidence from different jurisdictions where it wouldn’t be otherwise possible It allows the interagency cooperation and communication to perhaps solve crimes spanning several jurisdictions.

FT: Cool, and I bet it helps a lot with cold cases too.

PD: Oh, absolutely because evidence can be entered and then looked up later, or a gun can be recovered later, then test fired, and that information entered into the instrument. I don’t do that because it is solely law enforcement, and even when I work for a district attorney’s office I am still not working with that instrument, but that’s the concept just like it is for the fingerprint folks and the DNA folks.

FT: Hey, I’ve got to ask you, if you don’t mind and forgive me for going back to subject of TV. On the small screen, and in the movies, a bad guy, an assassin, or whoever will calmly select his prey, reach into his pocket, and pull out this a cylinder he will screw on the end of the barrel, and we all know it is a silencer, and it turns a loud bang into a soft POOT. How far off the truth is that?

PD: There are some very effective suppressors that reduce the report at discharge. The first thing that is a spoof on TV is, if the device is small, because they’re not – a small attachment isn’t going to work well, secondly, revolvers can’t be silenced because the noise would escape out the side between the cylinder and the barrel. Also, a threaded barrel is typically necessary to properly attach the suppressor and in all the cases that I have worked, I have only encountered a suppressed firearm twice. They are not common in casework but they do serve a legitimate purpose in the military, and I can even see advantages for them to reduce that annoying sound in a nonconfrontational venue as well. They’re not easy to make. It’s a federal offense if you make one without complying with all of the federal regulations for registration.

FT: Wow.

PD: Making a suppressor requires just as much skill as it takes to design and manufacture anything else that has an important job to do. It is not trivial if its not lined up exactly with the barrel. Making a homemade one is certainly not recommended because even if complying with all Federal regulations, it is being put right where the bullet is going to travel so, clearly it has to be well made, but there’s no universal suppressor that I know of that can just be simply installed on a firearm securely and safely.

FT: That makes sense.

PD: A suppressor has limitations based on the laws of physics such as the velocity of the bullet breaking the speed of sound and the pressure of the escaping gases. And again, they are very rare. I’ve worked only two cases that involved suppressors and both were on small caliber handguns ironically, both of them were homemade and neither worked properly. A suppressor certainly makes for a nice addition in a spy movie if portrayed accurately since there are legitimate reasons for their use.

FT: I had no idea. Hey, do bad guys, the typical criminals on the cases that you’ve worked on, do they ever take forensic counter measures beyond filing, trying to file off the serial number?

PD: I’m going to say yes in respect to trying to alter the microscopic information the firearm puts on the ammunition.

FT: Okay.

PD: Although not common, I do know of a couple of specific cases where I saw some marks that suggested alteration. Do I know that they were deliberate? I don’t. For all I know it could have been inexperience or some other thought process going on, but what I am getting at is, I have seen marks on firearms, whether it be firing pin, the breech face, the barrel, whatever it happens to be I have seen marks that were not incident to manufacture.

FT: Okay.

PD: I don’t know if those were forensic counter measures or not. Clearly, if the serial number is obliterated, that’s an obvious countermeasure. The serial number would not be scratched off if the person didn’t have some ulterior motive like hiding its owner. In other instances of damaged or altered markings I don’t know, if someone was trying to clean a part but did it incorrectly and managed to change it inadvertently. I have encountered that as well.

FT: I’ll be darned. Okay, now most of our readers are teaching at the high school level and some at college and they’ve all gone over lands and grooves with their students, but something occurred to me: it is difficult to set up and replicate and get students to do in classrooms is about trajectory. How important are these in investigations in real life? Do you see much call to figure that out or does it really not matter or does it never come into play?

PD: Oh, it definitely comes into play. In fact, a large part of my work goes well beyond suggesting whether or not a piece of ammunition came from the same firearm or a specific firearm. I enjoy the challenge of doing some sort of a trajectory or bullet path analysis and interpreting what the bullet has encountered during its flight based upon its damage or trace evidence on it. Trajectory is very important, and that’s some of the scenario you gave me about high school, it’s a great way of engaging students with an interest in geometry and trigonometry because those are important skills for the reconstructionist doing trajectory or bullet path analysis. The laws of physics are involved here, such as the kinetic energy of the bullet. It is giving up that kinetic energy as it travels. In flight the velocity is immediately decreasing as soon as the bullet leaves the barrel.

FT: Right.

PD: Gravity is immediately pulling the bullet downward so there’s no straight path as is sometimes suggested on TV. But it might be suggested and, admittedly, we use a straight line for shootings that take place in the room of a home because any downward path is negligible in that short distance. As the distance between the muzzle and the target becomes longer the trajectory becomes more curved as the bullet drops. Then a downward trajectory does have to be taken into account in spite of the laser beam, which of course, is not affected by gravity and remains a straight line.

FT: Gotcha.

PD: These reconstruction concepts provide some of the things that we do at John Jay College. We offer events over the summer, for high school and college students, where we try to incorporate a mock crime scene because the students can get involved and engage themselves. Then the instructors can see if the students were paying attention in mathematics and physics, which is incredibly important. We use laser beams, we use strings, probes, or the surveyors’ transit level in order to set up a potential path of a bullet for calculating where the bullet originated and then that information is used to support or refute witness statements or suspect statements about what happened. Luckily, the work that takes place, or that I do anyway, there is not an infinite amount of possibilities to consider. Because it is in a legal setting, the question to resolve becomes what one person claims versus what the other person claims and so on. If there is a big disparity between those two claims, often the evidence, which doesn’t have an agenda, might support or refute one side or the other, and the bigger the disparity between those two statements, the more you can suggest based upon a scientific interpretation of the evidence.

FT: I’ll be darned. I had no idea it was that important.

PD: In any event, remember Mark, I mentioned earlier that I really like to get involved in distance determination. Or interpreting trace evidence or physical damage to a bullet as a result of what it has encountered during its flight, and I have found that sometimes it is not initially appreciated. Sometimes the question of which gun fired which ammunition that’s more important, whereas other times there is no question which gun was fired but instead what did the bullet impact from when it left the muzzle to when it reached the target. It all depends on the facts of the case.

FT: Well, I’ll be darned. Okay, just a couple of questions about firearms in general because the topic of guns in schools is a tragic one and unfortunately in this day and age there are certain parts of the content that our readers don’t have access to and that is why I asked about trajectories and also what about gunshot residue? How long does it remain on one’s hand? Say you are using a revolver, is it hard to get off?

PD: Well, first of all, let’s have an understanding about gunshot residue. That term can apply either to residue from the primer, which is suggestive of what you mean because you mentioned hands. And the other is the propellant. You have primer residue and propellant residue that can often be included in the more broader term gunshot residue. So let’s start with the primer. The primer residue is a manifestation of the initiation of the firing sequence of the cartridge when the firearm is discharged.

In the classic sense, those items are the three elements lead, barium, and antimony, which if they were present in the primer compound, form a very stable and characteristic particle that is ejected from the firearm whether it be a revolver or a semi automatic or whatever – it can deposit itself on the person who is doing the shooting. It can deposit itself on the person near the person who is doing the shooting, and it could also be transferred from person to person. So, if someone has handled an item that had primer residue on it then that residue can be transferred to the person because the residue itself is transient in nature. It is very, very environmentally stable. The three elements were combined in a high pressure, high temperature environment to form the particle with the characteristic morphology and composition.

FT: Sure.

PD: They are somewhat spherical in nature, small particles, but they are not typically blasted or embedded into a person’s hand. In fact, you have greater likelihood that such a particle would remain for a longer period of time in a garment or in hair than you would on the skin. If deposited on the skin, when you do all routine things with your hands, such as opening doors or touching things the primer residue can be transferred.

FT: Uh huh.

PD: Combing or rubbing your hair or face is another example of potential transfer.

FT: Yup.

PD: The general consensus regarding particle retention is from about four hours to six hours, during which time those particles are in a steady decline. Most laboratories won’t bother looking for those particles after 4 to 6 hours post incident unless the hands of the suspect have been bagged, or the person is taken into custody very early or in a suicide case.

FT: Right.

PD: When the hands are bagged, or a person is in custody it limits how easy it is for those particles to get away otherwise a thorough washing even shortly after discharging a firearm will wash away so many of those particles that it wouldn’t be useful anymore to test for their presence, It also depends on the story that someone says. If someone says that they have never fired a gun, have never been near anybody shoot a gun, but then the test results reveal a few particles present on the person then that becomes probative.

FT: Right.

PD: In a different scenario, if the person does not say they were not near a firearm and you find a few particles, and they were in a car when a firearm was discharged or in a room where there had been a gun discharged nearby it would be an example of the positive results not being very useful. If you were in a car and there are four people in the car there is a likelihood that everybody who was present when the gun discharged may have some primer residue on them.

FT: Okay. All right.

PD: So primer residue particles are environmentally stable, but transient. That’s the golden rule with primer residue. Conversely, the propellant residue, also sometimes called organic gunshot residue, is used more to determine distance between the muzzle and the target, but it can also be indicative of the brand of ammunition since the exact composition varies among manufacturers.

FT: Oh.

PD: Just like the primer residue, the propellant can only travel a finite distance in air. Air is a tough medium to get through for a particle that has such a small mass and depending on the conditions and the kind of powder present in the cartridge, and some other factors such as ambient air movement, the maximum distance propellant particles can travel averages between two to five feet with rare exceptions. Sometimes it may not even travel beyond that distance because some small caliber firearms with not a great deal of propellant in their cartridges may only go out about two feet.

FT: Wow.

PD: Some large caliber rifle powders may go a little bit farther due to their greater mass, and here too ambient air movement can be a factor to increase or retard the distance traveled by the propellant particles. So, it’s very important for distance determinations to be aware of the ammunition, the firearm, and even environmental factors. The utility of performing a distance assessment can be expressed in a couple examples. Someone says an aggressive person was right on top of me about to clock me over the head with a sledgehammer so I fired at that person. When examined it is found that the victim, is loaded with gunshot residue propellant particles, then there is a potential confirmation of the survivor’s interpretation of what happened at that moment when the shot was fired

FT: Yup.

PD: As opposed to the opposite scenario, when there is not a single particle on that person who was shot and then you might inquire, ‘well how far away was this person when you were being attacked?’

FT: So tell me what’s a typical case like for a firearms examiner? Workload, expectations, that sort of thing?

PD: Well those are tough questions for me because I’ve never been in the trenches working as a firearm examiner in a crime lab.

FT: Ah, okay.

PD: I would imagine that you know in a big city like New York, there are plenty of firearm cases that come in and operability is the first thing that is performed because the folks who are assigned the case are deciding on the criminal charges so they have to know if a firearm is in working condition, and there is a certain time limit when charges have to be filed once a person is in custody. I don’t know whether that is 72 hours or something similar but the time frame is important. Within that period of time, it would have to be determined whether the firearm is capable of discharging a deadly projectile.

FT: Then what?

PD: If it is capable of discharging, then it would be test fired to obtain an example of a spent bullet and cartridge case; both for entry into one of the firearms databases to see if there are any other cases associated with that particular firearm and for comparison microscopy. If there are spent cases or bullets recovered from the crime scene or from autopsy then those can be compared to the test fired exemplars from the firearm.. If crime scene evidence is associated with that firearm, then that firearm may be associated through other means to an individual, such as fingerprints, biological material, trace evidence, or witness statements or whatever it happens to be, because the gun didn’t shoot the person by itself. Someone had to be handling the firearm. It all has to come together by the multidisciplinary actions of the crime lab. Unfortunately I can’t tell you about the workload, but I’m sure everybody would prefer to have more people to reduce the work load.

FT: Oh yeah.

PD: And to make sure everything goes smoother but I don’t really know how that goes.

FT: Do you happen to know after a case whether the person is convicted or not, what happens to the firearms that the police collect? Are they melted down?

PD: In my conversations with folks who are within the law enforcement community, many firearms are kept in what you could call a firearm library which is incredibly important. In my opinion, a firearm library can never be too big where an example of a specific firearm can be available for examination. Let’s say, hypothetically, you get a firearm as evidence in a shooting that maybe has a broken component and then, in order to make it work, you would take a piece of one from the reference firearm library and make it operable to obtain test fires. You can also use the reference library right off to train new people getting into the firearm section so they can become familiar with a wide variety of firearms. Since these reference firearms are no longer evidence in an active case, if a mistake is made in training disassembly or assembly its not catastrophic.

FT: Right.

PD: You are not dealing with evidence anymore with a reference library, but then every lab has only a finite amount of space. There is no unlimited room for anything, firearms included. At some point someone, and ideally someone who really knows what should be saved and what should be not saved, someone with that knowledge would have to go in and say, “take these guns, they are not needed. We already have samples of all these guns we’ll never need these again, and the case has been adjudicated long ago. We can melt these down.” But again, in my opinion, we can’t have enough books, hairs, fibers, sand, pollen, firearms, ammunition, or whatever it happens to be in a reference collection. It would be ideal to have the largest collection that space permits.

FT: I agree. What types of cases do you spend most of your time on?

PD: Mostly reconstruction. It’s a question of who did something and where they were at the time and where the victim was and that kind of thing. Often, it’s not whether or not this particular firearm fired this piece of ammunition, more often it’s who was doing the shooting and the distance between the two people, and could something have been in between, things like that.

FT: Do firearms examiners and tool mark specialists visit crime scenes or do they wait in the lab for someone to come back with their evidence?

PD: It’s kind of both, but unfortunately its more in the laboratory, and I am totally an advocate of having, if it is a shooting scene, someone who is firearms savvy to be at the scene especially if it is a complex situation.

FT: Why do you say that?

PD: Because as talented as the crime scene people are, there may be an expertise that the firearm expert can bring to a crime scene. It certainly wouldn’t hurt, and I’m not saying every single shooting incident, but if it is just a firearm being recovered, well then that’s pretty straightforward. However, if it is a complex shooting scene then an understanding of how the gun functions and cycles, the capability and maximum range of the ammunition, and things like that. These are the things that the firearm examiner is really good at it. A firearm examiner could offer something like, “Oh, you might want to look over here because this gun ejects its spent cases in this direction or its bullets have a certain amount of energy associated with them and could or could not have done a certain amount of damage. An example is an automobile I remember looking at.

There was what appeared to be a 5.56 mm M-16 type of bullet that supposedly hit this car straight on. Luckily, one person who looked at the car realized that kind of a bullet has so much energy, if fired at the car point blank it would have done more damage as opposed to it coming to rest right there in the outer part of the sheet metal. That suggested one of two things, either that bullet came from a really long distance or something got in its way and slowed it down, like a person, so it would have so much less energy by the time it got to the car.

FT: That makes a lot of sense.

PD: The tool mark community is even more complex because tools can leave marks that are not so easy to replicate because of the degrees of freedom in how a tool can be used or held. Just think: you’ve got a firearm and it is typically well made, and consequently there’s little room for movement of the ammunition inside the firearm. So the tolerances are well defined.

FT: Sure.

PD: But with tools, a screwdriver or a hammer for example, if you’ve got one in your hands, just look at all the different moves you can perform with your hand and that tool and then you have to replicate those marks to try to simulate for example a safe being smashed open. Or a door being pried open or something like that. It becomes challenging making the sample marks that were made by a tool so that requires considerably more patience and thought behind the making of the exemplar marks and the assessment of those marks.

That sometimes can’t be simulated properly unless there is a visit to the scene to get a feel for the substrate. If a screwdriver or a crowbar is pushed into brass or steel or a painted surface to pry something open there are tool marks and there is often trace evidence involved such as a transfer of paint or plating material or whatever from the substrate to the tool and that is where the trace examiner needs to be in harmony with the tool mark examiner.

FT: I never thought of that. I imagine you have been on the stand more times than you can count. Whenever I think of courtrooms, I think of the movie My Cousin Vinny.

PD: Oh that’s a classic; I strongly suggest that everyone in my class watches that both for the comedy and for the ending that includes the movie version of forensic testimony.

FT: Let me ask you again about forensic firearms examiners. What sort of training or experience is important for any of the students of the teachers who are going to be reading this? If they like solving mysteries like you said with guns and mixing them together and finding out what happened, what sort of training or education does that person want to pursue?

PD: Well, luckily there’s been a shift over time now to examiners requiring a science degree which is I think a big plus, especially when you have to consider all the things a gun does in order to work properly, in order to understand the discharge of the ammunition, especially in trajectories and bullet path analysis of a shooting scene. The firearm and the ammunition are bound by the laws of physics. Mathematics and trigonometry are absolutely necessary to perform a bullet path or trajectory analysis. In any event, there’s no single course that I know of that you can say, “Well, I took this course, and now I’m an examiner.” That just doesn’t exist. But I think anyone with a science degree has developed critical thinking skills during the course of obtaining their science degree and consequently they are better prepared to understand the principles of a sub-discipline whether it would be in firearm examination or another forensic specialty as well. Currently, the ATF, the Bureau of Alcohol, Tobacco, and Firearms, has a National Firearms Academy.

FT: Really?

PD: The National Firearms Academy is an opportunity for folks who are in law enforcement, if they are assigned to the firearms section, and their department sponsors them, can get involved in this National Firearms Academy where there’ll meet experienced people in firearms examination from around the country in addition to onsite expert staff from the ATF who teach the group. It is a neat system whereby the student examiners go to ATF headquarters and get their hands on training there, and then they go back to their departments to practice the skills and concepts learned. These examiner trainees then perform numerous exercises and report the results. Everyone is also required to conduct a research project which becomes the capstone experience and is often presented at a training conference

FT: Ahh.

PD: By obtaining the scientific training at the ATF laboratory and then gaining proficiency at the local laboratory level it doesn’t overburden the ATF because they have their own case load to do as well. But nevertheless, this system still provides a really thorough education for the folks who are involved in the academy. It is fortunate that it exists because otherwise training would be in the old fashioned way of the apprentice method, which has some drawbacks.

FT: Yes. That’s a fantastic opportunity, I had no idea they did that.

PD: The ATF has been running the firearm academy for several years and hopefully it will remain in spite of budgetary limitations, so folks who have the support of their departments can learn from the best.

FT: What was your favorite subject in high school and why?

PD: Remember in high school I was still looking to do chemistry as a career. I couldn’t, even in junior high school, get enough science, specifically chemistry, and same thing in high school and admittedly I had a one track mind when it came to learning more chemistry. For example, I wanted to figure out how propellants work. How the latent chemical energy within chemicals could be used to propel objects great distances

FT: Yeah.

PD: I was going to do the chemical engineering route, but then I veered somewhat when I read that book I mentioned earlier, Science Against Crime.

FT:You mentioned Dr. DeForest as being one of your most memorable teachers?

PD: Oh yes, there is no doubt about it.

FT: What made him so special? How did he approach the topic that really lit a fire in you?

PD: It was over time I guess, and I don’t even really think I appreciated the magnitude of Dr. De Forest until after school was over, because during school you just had to try to get good grades and do the best you could in your classes, but it was many years later where I was really able to appreciate just how brilliant he is and how he can use problem solving skills to figure out some of the most complex things. He would typically look at something and come up almost instantaneously with so many relevant questions about what needed to be investigated in a certain crime scene.

FT: I’ll bet that was amazing.

PD: It didn’t always have to be firearms either. He is adept at so many other forensic disciplines as well. I would be with him predominantly when he called me to consider a firearm case, but I’ve seen him in action in other types of cases as well, and it just boggles my mind how his critical thinking skills and problem solving is just unbelievable. He hates a mystery. He likes to unravel things. It’s truly amazing and I am honored to call him my professor and my friend. And obviously, my mentor as well.

FT: Sure, that’s just unbelievable you had a chance to study with someone that magical. That is fantastic. Do you have any advice for today’s science or forensic science teachers, how to keep kids turned on, to keep them hungry, to keep them wanting to put the pieces together?

PD: When I teach I try to tie in the theoretical with the practical by including some case stories where something has eluded me or others initially, and then after applying critical thinking skills that I have learned from Dr. De Forest and developed a little on my own, the solution became crystal clear once the right question was asked.

FT: Sure.

PD: Sometimes the right questions were never asked at the beginning and subsequently they finally are asked. Not to make an entire class full of war stories, but just to use them where they really tie in from the scientific concept to the case. It’s rewarding to hear a student say, “Oh wow, it really comes together, I see why that is important. I see why I have to learn that.”

FT: I love that.

PD: Dr. De Forest did that to us, he brought his casework to the classroom. And then I had the good fortune of hooking up with him again while in the Ph.D. program, I fully appreciated it, the way that he works, and the way he looked at things and I try to look at them the same way.

FT: I wish I had someone like that in grad school. Can I ask a few more gun questions?

PD: Sure.

FT: I was raised in a household where there were no guns. About a year ago a close friend of mine, who is a former Delaware State Women’s Pistol Champion, encouraged me and my wife to get into target shooting as a stress relief. So, we took a couple gun safety courses and I learned how to fire and be safe and clean them and that kind of stuff and I am just having a ball now, but the one thing I’m still having trouble keeping straight is, can you put a .357 round in a .38? And what’s the difference?

PD: The other way around.

FT: You can put a .38 in a .357?

PD: Yes, because the .357 magnum developed in 1935 by a collaboration of Smith and Wesson and, I believe Elmer Keith, creates considerably higher pressure than the .38 special cartridge. The .38 special was around for a few decades before that and the style of the revolver was still very popular in ‘30s and it was common to own or use one. It was easy to apply those shooting skills to something that simply had more power. So, Smith & Wesson decided to make a more robust version of the .38 special revolver that was popular back then which manifested itself into the S&W models 27 and 19 and others where the .357 magnum cartridge could be chambered. So, the reason that you can chamber the .38 special cartridge in a firearm designed for the .357 magnum cartridge is because the bullet diameter is the same, but the cartridge length on the .357 happens to be longer and it is longer on purpose. You have to realize that the .38 special cartridge case is not full of gunpowder. It does not develop very high chamber pressures compared to a .357 magnum cartridge. Since a .357 magnum develops much higher pressure than a .38 special, a revolver designed for the .357 magnum cartridge must be much stronger than one designed for a .38 special. It is safe to chamber the less powerful cartridge in the more robust revolver but never the other way around.

FT: Wow.

PD: The results would be catastrophic, so in order to ensure that a factory .357 magnum cartridge would never be chambered in a .38 special revolver, the manufacturers simply made the cartridge case about an eight of an inch longer.

FT: Oooooh.

PD: Yes, exactly. In so doing they’ve sort of built in the safety feature where if you did chamber it – you could put a .357 in a .38 special chamber, but what would happen is you would not be able to close the cylinder. The .357 magnum cartridge’s bullet would be protruding out the front of the chamber. That’s the safety feature that was incorporated into the manufacturing, and again it is because the frame of a .38 special revolver simply can’t hold back the extra 20,000 pounds of pressure that is developed in a .357 magnum cartridge. The same exact principle is used in the .44 special versus the .44 magnum. The .44 magnum came out in ’55. It is the Smith and Wesson model 29 and was made famous by Clint Eastwood in his Dirty Harry movies.

FT: Oh, yes.

PD: But in any event, the .44 special is a great practice round for those with a .44 magnum revolver just like the .38 special is a great practice round for those with a .357 magnum revolver. It makes for quieter shooting, less recoil, and more economical shooting.

FT: Yeah.

PD: You could still develop your targeting skills with the less powerful ammunition and then it is just a matter of firing a few rounds of the magnum ammunition to acquaint oneself with the pressure, noise, and recoil of the full power loads. So, that is my short answer which did not seem short (laughs), but that’s my short answer to your question about co-mingling calibers, it is not often that one can do that. Those are two very popular calibers where that can be done. By the way, in a revolver that’s chambered for a .22 long rifle cartridge you could chamber .22 shorts. Just be aware that it is necessary to thoroughly clean the chambers when you’re done shooting.

FT: Really?

PD: Yes, the reason for this is if you fired a lot of .38 specials in that .357, or a lot of .44 specials in a .44 magnum, what happens is there is a little bit of residue that builds up in the very, very far end of the chamber because there’s no cartridge case there. There is an area where the discharge components can accumulate. So, what will commonly happen is if you fired a couple hundred rounds of the shorter ammunition, you may have to force your magnum load into the chamber because they’re longer, and now it gets in the way of some leading, some propellant residue. So, if you have to force them in it stands to reason you’ll have to force them to get them out.

FT: I hadn’t thought of that.

PD: You don’t want to go to battle if you have to reload then you can’t get your empties out. So, hypothetically, if you’re a trooper, and that was your duty gun, you were carrying a .357 on your hip and you did a lot of practice shooting over the weekend with .38’s, then I would run a brush through each one of those six chambers to make sure your duty ammunition is going to slide in and slide out very quickly.

FT: Oh, yes. I understand how that could be very important. Hey, you mentioned some high school workshop or workshops for high school teachers at John Jay College?

PD: Yes. There were some folks at Jay whose job it is specifically to arrange and coordinate these outreach activities. I think its call the STEM program.

FT: Oh yes.

PD: John Jay College also offers a program called College Now to students from any City high school to get a taste of college. It’s a longer program delivered over several days during the summer by the instructors and staff in the Department of Sciences. They are very talented people who teach the students about molecular biology, in which I am not at all fluent, and physics and math and then sometimes in my discipline, forensic science. The idea is just to stimulate their interest and appreciation of science.

FT: Neat.

PD: By necessity the students have to come to John Jay for these programs because we include hands-on exercises and demonstrations to dispel some of the myths of what they see on TV. It’s the real thing. They will charge them a minimal amount of money to cover the materials we consume like fake blood, or if I go to the range and make some test fires, and they get to take their bag of science goodies home. We give them gel lifters, litmus paper, little things they may not have in their own schools. I was surprised to hear that sometimes in these other high schools they have far more limited resources than my high school had. So, we try to give them something to think about when they leave.

FT: And you’re going to send photos for this article?

PD: I can. Remember Mark even though I’ve done the traditional comparison microscope work, I am also an advocate (as I get on my soapbox) for having a bullet tell the complete story. That includes impact damage and trace evidence transfer. I can send you a bunch of different things like a pattern on a bullet because the bullet hit a zipper or it hit a screen. These are times when a bullet is recovered at a scene or at autopsy and it has a peculiar mark or impression on it. Initially you can’t figure out what caused the marks or what it went through and then you look at it closer and say, “holy crap, look this is from a zipper.”

FT: I’ll be darned.

PD: Yes, it’s really rewarding to figure out these non-routine cases. Every time I do one of these complex cases, where the work with Dr. De Forest comes in, you just have to appreciate the science behind the interpretation. Dr. De Forest rarely did the routine stuff. The same applies to my other professors at the College who I named earlier. The routine stuff is either pled out or it never goes to trial. But the non-routine stuff, that’s where it gets complex requiring critical thinking and problem solving skills. For example a paint chip on the bullet, or its impact orientation meant something about reconstructing the incident.

FT: Gotcha.

PD: So, a bullet is very, very easily destabilized by interacting with something, the first thing it runs into, and then may come to rest in someone or something else, and its an appreciation of this that I learned from Dr. De Forest and my own tests fires where I used high speed photography to understand these dynamics. That’s what I bring to the classroom when possible, but I also bring it to the courtroom. Many times there’s a question that we can answer with some scientific experimentation.

I can share with you a link to a case that I worked with Dr. De Forest recently. It was covered by the New York Times. It was a tragic case that involved the death of a person where we disagreed with the interpretation of the evidence. The link is

FT: We’re digital so we’re not short on space. Typically our readers are hungry for content because 95% of them have no experience with handguns or guns at all. What they know is what they see on TV and so do most of their students.

PD: I’m glad I could help.


Dr. Peter Diaczuk knows guns. He knows bullets. He knows where they live, the company they keep, and what sort of tricks they can pull when an investigator isn’t looking. He knows ricochets and what they’ll do to a projectile. In short, he really, really knows firearms. In fact, he is the director of Forensic Science Training at the Center for Modern Forensic Practice and instructor in the Department of Science at John Jay College of Criminal Justice. He is also a Diplomat of the American Board of Criminalistics, and a Fellow of the New York Microscopical Society. In short, Diaczuk has forgotten more about firearms than you and I or even doomsday preppers will ever know.

By Mark Feil, Ed.D.