Ask any assault lawyer in Arizona who knows the law. Just because a suspect tests positive for GSR doesn’t mean he shot his victim. In fact, the tenets of GSR are so shaky that an assault lawyer has many opportunities to insert doubt over such evidence, making it practically useless in a court of law.
What is GSR?
The Trace Evidence Procedures Manual defines GSR (short for “Gun Shot Residue”) as “a particle with a spherical or molten appearance containing the elements Pb, Ba, and Sb.” The reality is that 99% of the time, neither the police nor the assault lawyer in Arizona actually tests for gunshot residue. Instead, they test for primer residue.
To understand GSR, let’s first take a look at gunpowder. Essentially, it’s combination of chemicals that, once ignited, burn at a predictable rate, expanding gases that create pressure and force the bullet down the barrel of a gun. In the early days, gunpowder was a black powder that 75 % potassium nitrate, 15% charcoal, and 15% sulfur. Nitrate is the base fuel of all gun powders, though they may take several different chemical forms. Gun powder has advanced over the years to include other ingredients, but at its base it is essentially the same.
Crime scene investigators take a swab sample from a person or article and test for a combination of chemicals from gunpowder residues, primer residues and lead residues. It is important to note that increasingly, companies are making gun powder with less or no lead residue in its ingredients. This is done in order to make shooting safer in an indoor arena, as lead free ammunition keeps the shooter from inhaling the toxic metal and risking cancer.
Problems with nitrates
Nitrates are the fuels that make the gunpowder burn. The problem that is of interest to an assault lawyer is that it is quite possible to test positive for nitrates by coming into contact with an endless stream of everyday ingredients, with fertilizers and fuels topping the list. In fact, obtaining a false positive test is so easy that most police departments these days don’t even bother to test for nitrates. They just aren’t reliable.
When the powder remains, soot is what remains. You can get soot from car exhaust, fireplaces, even a cigarette. Testing positive for soot should hardly require the need to hire an assault lawyer.
Problems with primers
Primers are the small cups or circles on the base of the cartridges that ignite the gunpowder with a small explosion – just like a child’s cap gun. This is where the job of police work gets interesting and where an assault lawyer should take notice. Most primers contain the chemicals barium nitrate, lead styphnate, and antimony sulfide. There are a number of chemicals the forensic expert must identify. The fact that they do not identify all chemicals does not mean it is not GSR, and even if they do, it does not mean that the person fired the gun. GSR is based upon shaky, questionable grounds that an assault lawyer can bring to the court’s attention in the best interest of his client.
GSR is a very inconclusive piece of evidence that is being questioned more and more by the courts. An assault lawyer in Arizona should always insert doubt into any presented testimony of GSR. The evidence is simply not valid or sound enough to base a judicial decision upon.
About the Author
David Michael Cantor is an AV rated (the highest possible rating) lawyer and a Certified Criminal Law Specialist per the Arizona Board of Legal Specialization. For more information about an Arizona assault laywer, visit our site.