The Particle Articles

On January 22^nd, Dave Exline, Senior V.P. and Rebekah Wagurak, Forensic Scientist at Gateway Analytical, hosted a webinar designed for police and attorneys and built upon the information provided in our previous webinar, “Forensic Analysis of Gunshot Residue for Police & Attorneys.”  During this webinar, our presenters provided police officers with tips on the proper collection of gunshot residue (GSR) evidence, as well as, the methodology used to analyze and interpret the data utilizing automated scanning electron microscopes (SEM).  Our presenters also took attendees into the courtroom, providing attorneys with insight into the significance of GSR evidence during a case, and what implications can be made from this type of evidence during expert testimony.

For more details on the webinar, you can use the links below.

• View the webinar
• Download the presentation slides

We received a number of questions from attendees during the Q&A segment, and you can find those questions and answers below. If you have any questions about this or any other topic, please contact us.

1. Are Barium, Antimony, and Lead considered primer residues as opposed to GSR or have law enforcement and analytical labs gone back to using term GSR due to specific protocols?
   I believe at the start of the webinar, Dave clarified that we would be discussing primer gunshot residues, which is what we would use synonymously with the term primer residues. So yes, what we are discussing today as “GSR” are actually primer gunshot residues, as Dave mentioned.
2. Can GSR particles be destroyed during collection with the stubs?
   Particles can be broken, as I mentioned when discussing morphology checks. Sometimes you will see a spheroid particle, with one side that was obviously broken off and has some jagged edges. How these particles are broken can vary. I would think that generally the action of stubbing would not cause a lot of particle breakage, as it is a soft adhesive and these are extremely small particles; but I would not say that it would be impossible either.
3. Are NAA, AAS, and ICP-MS considered destructive testing methods?
   Yes they are. Solvents are used, and the samples are consumed during analysis.
4. Does bagging the hands make a difference on the timeline of collection for GSR evidence?
   Bagging of the hands is more or less used to minimize the risk of contamination. I can’t speak to collection times, as we don’t perform the collection. Each agency or police department has their own standards on time limits. The concept of bagging is focused on not adding GSR to a hand from the environment (like a police car). It is not really a tool to extend the collection time.
5. As an examiner, have you included SEM photos with your lab reports?
   Generally we don’t provide SEM photos with our gunshot residue analysis lab reports, unless it is requested.
6. Is it becoming more common for labs to no longer accept GSR cases since the results do not provide any kind of confirmatory information regarding the discharge of a firearm?
   Not really; GSR is a type of trace evidence. And like most trace evidence, it is a class type of evidence. It is used as a tool to help created investigational leads, build cases, etc. While it typically is not used alone, it can be really helpful when used in conjunction with other types of evidence. Some labs may not do GSR because they don’t have an SEM, or can’t get one due to budget concerns; in these cases, subcontracting would be an option.
7. Does the testing process still take several hours? What is length of time for automated vs manual parts of the testing?
   The automated run will take several hours. The more particles containing lead, barium, and/or antimony present on the sample, the longer the automated analysis will take. This is because the instrument will collect on these particles for a short period of time before moving on. If you have a relatively “clean” stub, automated analysis will go quicker. The manual checks is dependent on a lot of things, such as expert experience, how loaded the samples are, how straightforward analysis is, etc. Usually manual checks will take at least a few hours, give or take.
8. If hands are bagged, do you need bags submitted as well?
   Generally, that is not common practice. Only stubs will be submitted. Again, the bags serve to reduce contamination risks; not to catch particles.
9. Can you compare GSR samples taken from suspect to GSR that is created from known ammunition found at the crime scene?
   This can be done; and it might be of interest to do this, especially in the cases that involve more unusual types of ammunition (such as lead-free and tagged ammunitions).
10. Can you see GSR on clothing by just looking at it?
    No; as Dave mentioned, these particles are on average 1-20 microns in size. This is well beyond the threshold of the human eye’s seeing ability. What you may see on an article of clothing might be unburned/partially burned gunpowder particles around a bullet hold. In order to see GSR, however you will need a high powered microscope like an SEM.
11. Can you determine distance of shooter from victim by looking at the number of GSR particles present on the victim?
    No. As mentioned, there are many reasons that may contribute to presence/absence of particles. All we can speak to as GSR experts would be whether or not primer gunshot residue was present on the sample. There are other methods that are employed for distance determination and they would involve performing a test fire.
12. Can you determine if a revolver or pistol was fired based on the amount of GSR found on a suspect?
    No. Again, there are many reasons that may contribute to the number of particles present. While a particular firearm might tend to deposit a lot of particles onto a shooter, the shooter may have washed his hands and there might not be that many particles on him. Again, the expert can only speak to the fact that there was or was not GSR present on the sample.