By Zack Wavrusa
Assistant County & District Attorney in Rusk County
If you have been a prosecutor for more than a minute, you have surely heard of the “‘CSI’ effect.” It is the tendency of jurors to have unrealistic expectations of forensic science in a criminal trial because of what they see on TV (especially “CSI” and its iterations). The modern prosecutor must consider this effect in everything from grand jury presentment, to voir dire, to closing arguments.
But what if I told you that even prosecutors and law enforcement are influenced by the “CSI” effect? Yes. Prosecutors and peace officers are just as likely as jurors to have unrealistic expectations about forensic evidence collected during criminal investigations. The effect in law enforcement and prosecution is arguably more harmful because we all know just enough about forensic sciences to think of ourselves as immune.
In my experience, gunshot residue (GSR) testing is a good example of this phenomenon at work. People in our profession can sometimes have overblown expectations about what, if anything, GSR testing can add to our cases. We have a responsibility as prosecutors and law enforcement officers to know what GSR testing is, how it can help resolve fact issues in a criminal investigation, and how to use that evidence effectively at trial.
What is GSR?
Firearms use an explosion to propel projectiles toward their intended targets. During the discharge of a firearm, escaping gases from the weapon deposit residue on the skin of the shooter’s hands, on his or her clothing, and on other objects in close proximity. Included in this gaseous cloud are particles composed mostly of primer residue. Primer compositions may vary with different types of ammunition and manufacturers, but the most common constituents of primers are lead styphnate, barium nitrate, and antimony sulfide. It is unlikely that the presence of these articles would be visible to the naked eye. Their detection requires law enforcement to take swabs from the area of interest (usually a suspect’s hands) and submit those swabs to a lab for forensic testing.
What can GSR analysis do for you?
The strength of a GSR test comes from its ability to associate an individual with a firearm discharge when that person has not otherwise been associated with a weapon. Analysis and characterization of the residue for the trace elements (lead, barium, and antimony) may indicate if a suspect has fired, handled, or been in close proximity to a weapon when it was fired. In some instances, analysis of inanimate objects, such as clothing or vehicles, can yield helpful information for an investigation, as particles can transfer from a surface to a person or vice versa.
The DPS Customer Service Handbook cites four instances where GSR is particularly useful:
1) to support or refute a statement or witness information;
2) to answer lingering questions after other laboratory analysis has been performed;
3) when DNA, fingerprint examination, or firearm analyses have not indicated one suspect over another; and
4) when firearms analysis has identified which gun was used to shoot the victim but no fingerprint was recovered from the gun.
Unfortunately, the circumstances in which GSR analysis can be informative are pretty limited. Prosecutors may want or expect GSR to tell us many more things that the science simply cannot. For example, a GSR test does not indicate the distance from which a firearm is fired. Distance determinations are possible, but a GSR test is not the method that DPS will use for such a determination. A GSR test is similarly unhelpful when performed on a shooting victim because the victim has obviously been associated with a firearm.
A GSR test is also unhelpful in making a suicide vs. homicide determination. This is because more gunshot residue escapes the barrel of the firearm than near the grip, meaning that someone who is shot by a firearm may have substantially more GSR particles on himself, including on his hands. The majority of homicide and suicide victims will have gunshot residue on their hands, and a very small percentage of both homicide and suicide victims have no gunshot residue on their hands. For this reason, neither the presence nor absence of gunshot residue will provide a definitive interpretation of either a homicide or a suicide.
GSR and the Fourth Amendment
For purposes of the Fourth Amendment, there isn’t anything unique about searches for GSR. If you find yourself fighting the suppression of GSR evidence, there are a couple of helpful cases, depending on the circumstances.
When officers seek a warrant to obtain GSR evidence, the preferred practice is to say so with particularity in the warrant and affidavit. If this practice was not followed, hope is not necessarily lost. The Court of Criminal Appeals has held that the specificity required for a valid search warrant is flexible and will vary according to the crime being investigated, the item being searched, and the types of items being sought.[1] To determine whether a search and seizure falls within the warrant’s scope, we follow a common sense and practical approach rather than an overly technical one.[2] A warrant that fails to describe “the items to be seized at all” is “plainly invalid.”[3] A warrant’s description of items to be seized is sufficiently particular, however, if the officer executing the warrant will reasonably know what items are to be seized.[4] A warrant that does not specifically list “gunshot residue” as an item to be seized is not necessarily invalid. When the warrant lists items such as “firearms, firearm magazines, other ammunition storage devices, and ammunition itself,” courts have found this language to be sufficiently particular to authorize the search and seizure of GSR evidence.[5]
It is also possible for a warrantless search for GSR to be proper under the right circumstances. In an unpublished opinion, the Fourth Court of Appeals held that the threat of rain coupled with the fragile nature of gunshot residue itself was sufficient to trigger the exigent circumstances exception to the Fourth Amendment’s warrant requirement.[6] The Department of Public Safety’s requirement that swabs be taken within four hours of a weapon’s discharge definitely increases the likelihood of exigent circumstances arising, especially in rural jurisdictions where the manpower and tools to get a warrant quickly are not always available.
DPS criteria for GSR testing
Despite what crime scene investigators might do on TV, DPS labs won’t even test for gunshot residue except in certain instances. DPS testing is limited to cases involving crimes against a person, specifically, homicides, aggravated assaults, aggravated robbery, and “questioned death or death investigation cases” as appropriate for GSR testing. A questioned death is where there is a question whether someone’s death was a suicide; in those instances, DPS will not run the victim’s kit, but the lab would potentially analyze any suspects or elimination samples if doing so might lead to helpful conclusions. Cases involving deadly conduct are assessed on a case-by-case basis.
If the DPS lab determines that a GSR analysis will not yield results with useful interpretations, the evidence will be returned to the law enforcement agency, and a “Closed Without Analysis” report will be issued to explain the laboratory’s decision. DPS will generally return GSR kits without analysis on cases of suicide, discharging a firearm in city limits, and felon in possession of a firearm, absent some documented extenuating circumstances. If DPS makes this determination based on its policies and procedures, it requires a written request from the prosecutor or a valid court order for testing to be performed. If this request results in the laboratory confirming the presence of GSR, the report will state that no interpretation can be provided by the laboratory.
How GSR analysis is performed
Before testing can take place, swabs of the suspect’s hands must be collected within four hours of the incident in question, before the suspect’s hands are bagged. (Law enforcement will sometimes place bags over a suspect’s hands to prevent the loss or contamination of evidence, such as blood or skin cells trapped underneath a suspect’s fingernails, until it can be properly collected, but gunshot residue will likely be wiped away by the bag’s contact with the suspect’s hands.) After the swabs are collected, law enforcement should submit them to the appropriate DPS crime lab along with a copy of the Gunshot Residue Kit Information Form (LAB-211). At a minimum, this form needs to detail the date and time of the incident, the date and time the GSR kit was collected from the subject, whether the subject was shot, and whether the subject had a firearm on his or her person when detained.
DPS testing for GSR is done by Scanning Electron Microscopy–Energy Dispersive Spectrometry (SEM-EDS). SEM-EDS testing has become the preferred method of analysis over techniques like atomic absorption because SEM-EDS provides increased specificity and allows the analysis to be conducted without chemicals.[7] SEM-EDS analysis has been used in GSR analysis since the 1970s, and it allows for the identification of GSR particles based on morphology and composition. There are two types of particles that this test will reveal: characteristic and indicative.
Characteristic particles are three-component particles made of lead, barium, and antimony. Indicative particles are two-component particles composed of lead and barium, lead and antimony, and barium and antimony. The DPS Customer Service Handbook lists a variety of sources for both characteristic and indicative particles that go well beyond firearms. These sources range from the unsurprising (think fireworks and flare guns), to shocking (recycled brown butcher paper and car radio components). If you are working on a case involving GSR, you would be wise to evaluate the list of “GSR particle contributors” in the DPS handbook to see if any of them might apply to your case. If they do, talk to the forensic scientist who performed the examination because these non-GSR materials often contain additional elements that are inconsistent with GSR identification.
What does the difference between characteristic and indicative particles mean in terms of the conclusions a DPS forensic scientist can reach? According to DPS, the presence of characteristic particles is consistent with the person having recently 1) fired a weapon, 2) been in immediate proximity of a weapon as it is being fired, or 3) come into contact with a surface containing gunshot primer residue particles. The presence of indicative particles is consistent with any of the following:
• particles originating from an environmental source;
• characteristic particles being deposited but later removed;
• a weapon or ammunition that does not consistently produce characteristic particles but only indicative particles; and
• a person coming in contact with a surface that had indicative particles.
GSR testimony
The major difficulty with GSR testimony lies in the fact that while forensic scientists can report that the particles came from a fired weapon, they cannot describe how they were deposited on the person or item. Similarly, forensic scientists cannot identify the person who discharged a firearm in the commission of a criminal act. As mentioned earlier, a positive GSR finding is most probative in cases where a suspect denies proximity to a discharged firearm because GSR is not common to the average person’s daily environment.[8] A negative finding does not rule out the possibility that the subject was not in the vicinity of a recently discharged firearm; it indicates only that no evidence of primer residue was found on the items tested.[9]
A defense attorney may raise questions at trial as to why GSR was not collected and later argue that negative results would have exonerated his client. Do not let this potential argument serve as the sole reason in requesting a GSR examination that falls outside of DPS’s protocols—there is a good chance that the results raise more questions than they answer. To counter this type of claim, there may be circumstances where a prosecutor must designate a forensic scientist from DPS to explain the limits of GSR testing to the jury and how the facts of the case before them was not appropriate for GSR testing.
Conclusion
Being an effective prosecutor requires us to know what tools are available to us and the extent of those tools’ usefulness. The forensic sciences are some of the many tools at our disposal, and it is important to know how much information they can reveal to utilize them effectively. For that reason, prosecutors who find themselves working on a shooting case should familiarize themselves with the limits of GSR analysis and the testing policies and procedures of the crime lab. Don’t fall into the trap of relying on what you think you know when it comes to the forensic analysis of GSR particles. The science behind GSR analysis has its limitations, and prosecutors would be wise not to let the “‘CSI’ effect” convince us that answers can be provided to questions that are beyond those limitations.
Endnotes
[1] Gonzales v. State, 577 S.W.2d 226, 228-29 (Tex. Crim. App. 1979).
[2] State v. Elrod, 538 S.W.3d 551, 556 (Tex. Crim. App. 2017) (magistrate may use logic and common sense to make inferences based on facts in affidavit).
[3] Groh v. Ramirez, 540 U.S 551, 557-58 (204).
[4] Balderas v. State, 629 S.W.3d 610, 614 (Tex. App.—Houston [1st Dist.] 2021, no pet.); Harmel v. State, 597 S.W.3d 943, 962-63 (Tex. App.—Austin 2020, no pet.).
[5] See Gonzalez v. State, 616 S.W.3d 585, 594 (Tex. Crim. App. 2020), cert. denied, Gonzalez v. State, No. 21-5327, — S.Ct. —, 2021 U.S. LEXIS 5435, 2021 WL 5043646, at *1 (Nov. 1, 2021).
[6] Johnson v. State, No. 04-13-00766-CR, 2014 Tex. App. LEXIS 13701, at *10 (Tex. App.–San Antonio, Dec. 23, 2014).
[7] https://leb.fbi.gov/articles/featured-articles/the-current-status-of-gsr-examinations.
[8] Id.
[9] Id.