Gun Shot Residue

By Christina, Kendra, and Nathan

Gun Shot Residue (GSR) is the substance left behind when a firearm was used.

Physical Properties

  • Can consist of both burned and unburned primer or powder components
  • If it's burned, it does not have a distinguished color, or shape
  • Burnt, it could be a powdery substance.
  • It smells like gunpowder if you can even smell it at all.

Chemical Properties

  • Major three elements are lead (Pb), barium (Ba), or antimony (Sb)
  • Less common elements include aluminum (Al), sulfur (S), tin (Sn), calcium (Ca), potassium (K), chlorine (Cl), copper (Cu), strontium (Sr), zinc (Zn), titanium (Ti), or silicon (Si)
  • Reacts with nitrate residue
  • Burns by reacting with potassium

Case Study: People v. Contreras, 1998

On a December night in 1998, a woman named Delia Rabina Contreras called 911 to inform them that her boyfriend Anselmo Vasquez had shot himself and was in critical condition. Contreras claimed, on the phone, that he had been shot in the head, but the bullet wound found on the body was in the chest. Upon further investigation, it was discovered that Vasquez’s hands were covered in gunshot residue and that she had lied about many other details of the murder. The GSR on her hands was the biggest evidence they had against her, but she was eventually convicted of her boyfriend's murder.
What gunshot residue tests tell us

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