Unit 5: Firearms, Tool Marks, and Other Impressions Mr. Ross Brown Brooklyn School for Law and Technology

How can we determine the firearm from which a bullet was shot? 18 April 2016 Do now: What makes it difficult to determine which firearm shot a specific bullet?

In this unit we will learn about: How to compare bullets Information we can gather from cartridge cases Gunpowder residues Primer residues on the shooter’s hands Firearm serial numbers Tool marks Other impressions

How can we determine the firearm from which a bullet was shot? Just as fingerprints can tell us apart, inanimate objects also have specific markings Scratches, nicks, wear patterns Firearms identification

How can we determine the firearm from which a bullet was shot? Bullet markings Gun barrels are rifled, or created with grooves Grooves give a fired bullet spin so it flies true

How can we determine the firearm from which a bullet was shot?

How can we determine the firearm from which a bullet was shot? Caliber is the diameter of a gun barrel measured between lands Typically in hundredths of an inch or millimeters

How can we determine the firearm from which a bullet was shot? 19 April 2016 Do now: In addition to rifling marks, what other markings identify the weapon which fired a bullet?

How can we determine the firearm from which a bullet was shot? Lands: raised portion between grooves in a rifled barrel Grooves: Low-lying portion between lands Rifling: Spiral grooves formed or cut into the barrel of a rifle or gun to spin the projectile

How can we determine the firearm from which a bullet was shot?

How can we determine the firearm from which a bullet was shot? Cartridge cases Just as bullets show deformation, so too do cartridge cases from contact with metal surfaces

How can we determine the firearm from which a bullet was shot?

How can we determine the firearm from which a bullet was shot?

What else can we use to identify a weapon used in a crime? 21 April 2016 Do now: Why is gunpowder residue an important piece of evidence?

What else can we use to identify a weapon used in a crime? How a bullet works

What else can we use to identify a weapon used in a crime? Gunpowder residue Helps determine firing-distance How far away was the shooter? Could this have been self-defense?

What else can we use to identify a weapon used in a crime? Primer residue on hands Used to put hot wax on the suspected shooter’s hands to find nitrates (in the gunpowder) Today, we test for chemicals only found in the primer

What else can we use to identify a weapon used in a crime? Serial number restoration The pressure applied while grinding the number in fact presses it into the body of the weapon Acid can etch out this weakened metal

What else can we use to identify a weapon used in a crime? Considerations when collecting firearms evidence Safety! Mark bullets for identification, but only on nose or base to protect rifling marks Of course, everything tagged, numbered, etc Bring to lab quickly