Key Concepts

  • A gunshot residue (“GSR”) wipe test detects the presence of distinctive chemicals that are deposited on a person’s skin or clothing or other nearby surfaces when a gun is fired.
  • GSR tests results are considered reliable, and should be admitted into evidence.
  • Gunshot residue can be removed by actions such as washing hands, wiping clothing, or brushing it off, so the absence of residue does not prove that the person did not recently fire a gun.

Overview 

When there is reason to believe that a suspect may have recently fired a gun, he or she can be given a “handwipe” or similar test, which is a type of gunshot primer residue test (often referred to as a “GSR” test), to detect the presence of certain chemicals that are deposited on nearby surfaces when a gun is fired. For a more detailed explanation of how gunshot residue is created and how the handwipe test detects it, see, e.g., Dr. Allison C. Murthalinxian Wu, The Science Behind GSR: Separating Fact from Fiction,” Forensic Magazine, September 27, 2012.

In short, when a person pulls the trigger on a gun, this causes the firing pin to strike a “primer” located at the base of the cartridge. That primer strike, in turn, sparks a chemical reaction inside the cartridge that ignites the gunpowder, and the resulting explosion propels the bullet out of the barrel of the gun. The smoke and gas that comes out of the gun along with the bullet typically contains particles of unburnt gunpowder, tiny bits of metal, and signature chemicals from the primer mixture (usually lead, antimony, and barium), which get fused together from the heat of the firing and settle on the person’s skin, clothing, and other nearby surfaces. The GSR test detects the presence (and quantity/amount) of these distinctive chemicals, which indicates that the person: (i) recently fired a firearm, (ii) was in very close proximity to the gun when it was fired, or (iii) came into direct physical contact with the person who did fire it (this is less common, and fewer particles will be detected).  

There is no scientific test currently available to determine whether a particular gun has been recently fired – the available testing only determines whether there is residue from a recent firing on the person’s skin, clothes, etc. It is also important to note that the absence of GSR does not prove that a person did not fire a gun, since the residual chemicals can be removed by wiping, hand-washing, wind, rain, etc. See State v. Lambert, 341 N.C. 36 (1995) (“negative gunshot residue test could be explained by defendant's wringing of her hands and the use of her hands to wipe tears from her face”).  

Reliability and Admissibility 

Cases decided both before and after the 2011 amendments to Rule 702 adopting the Daubert standard have held that a properly qualified witness is permitted to testify about performing a GSR test, and give an opinion as to what the results of that test indicate (e.g., the likelihood that the defendant fired a gun, handled it shortly after it was fired, or was in close proximity at the time it was fired). See State v. Daughtridge, 248 N.C. App. 707 (2016) (post-Daubert amendment case, approving admissibility of expert opinion which relied in part on GSR test results); State v. Sparks, 297 N.C. 314 (1979) (forensic chemist was properly permitted to testify that tests performed on defendant’s trousers showed the presence of nitrites, and that nitrites were produced by burned gunpowder; chemist also properly was permitted to testify about gunshot residue found on defendant’s left hand); State v. Tilley, 292 N.C. 132 (1977) (properly qualified witness permitted to testify that defendant “probably” or “could have” fired a gun, based on results of test); State v. Crowder, 285 N.C. 42 (1974) (GSR test used in this case “demonstrably possesses the degree of reliability required to render it competent. We hold that evidence of the results of the test was properly admitted”), vacated in part on other grounds428 U.S. 903 (1976); see also State v. Barnes, 345 N.C. 184 (1997) (“…the gunshot residue evidence tended to show that Barnes shot the Tutterows. The evidence revealed that Barnes had fired a handgun or had handled a handgun soon after it was fired within a period close to the time of the killings”); State v. Benjamin, 83 N.C. App. 318 (1986). (expert permitted to testify that presence of GSR on victim’s hands “could have” come from victim raising his hands in a defensive posture, and absence of GSR on defendant’s hands “could have been caused” by passage of time and defendant’s actions in between the shooting and the test). 

The person who collects the GSR wipe or sample does not have to be qualified as an expert – the state only needs to show that the person knew how to collect it properly and did so in this case. See State v. Crowder, 285 N.C. 42 (1974)vacated in part on other grounds428 U.S. 903 (1976) (SBI agent was qualified to take gunshot wipe from defendant’s hands when procedure was not “highly technical,” the agent’s background included technical police investigatory work, and agent was given personal instructions by chemist who was an expert with gunshot residue tests); see also State v. Oakes, 113 N.C. App. 332 (1994) (applying similar rationale to an officer who performs a simple field test on suspected drugs). 

Exigent Circumstances 

A gunshot residue test is considered a nontestimonial identification procedure, similar to taking a photograph or obtaining a voice sample, so whenever possible a nontestimonial order or other court order should be obtained before administering the test. See State v. Coplen, 138 N.C. App. 48 (2000) (like other procedures described in G.S. 15A-271, “a gunshot residue test is a relatively non-intrusive procedure” and it “falls within the broad language [of] ‘similar identification procedures’ in that it is comparable to handwriting exemplars, voice samples, photographs, and lineups”). 
However, because a gunshot residue wipe must be taken within a few hours of the shooting to have any value, and because the residue can be easily removed or destroyed by normal activities such as hand-washing or reaching into a pocket, appellate courts have upheld the admissibility of GSR tests done in the absence of a court order based on a showing of exigent circumstances and probable cause. See, e.g., State v. Page, 169 N.C. App. 127 (2005)State v. Coplen, 138 N.C. App. 48 (2000)

Admissibility of Refusal? 

At least one state Supreme Court case has specifically held that if a defendant refuses to consent to a GSR test, the fact of that refusal is admissible at trial as evidence of guilt. See State v. Odom, 303 N.C. 163 (1981) (evidence of defendant’s refusal was properly admitted at trial: “In conclusion, we hold that the admission of testimony concerning defendant's refusal to submit to the gunshot residue test did not violate her constitutional right to counsel and did not deprive her of due process of law.”).  

However, this holding appears to be in conflict with the general principle expressed in other cases which have held that when a defendant exercises his or her rights by refusing to consent to a voluntary procedure, it is error to admit that refusal into evidence. See, e.g., State v. Davis, 235 N.C. App. 424 (2014) (unpublished) (“North Carolina law bars the use of a defendant's exercise of his or her constitutional right to be free from an unreasonable search to imply guilt”); State v. Steele, 160 N.C. App. 710 (2003) (unpublished), citing State v. Jennings, 333 N.C. 579 (1993), cert denied, 510 U.S. 1028 (1993) (“It is constitutional error to admit testimony as evidence of guilt that a defendant exercised his constitutional rights and refused to consent to a warrantless search.”).