Forensics Chapter 16 - Tool marks and guns

Striation

Fine lines found in the interior of the barrel

T or F; Shotgun shells are NOT impressed with striations

TRUE

T or F; the act of pulling the trigger serves to release the weapon’s firing pin, causing it to strike the primer, which in turn ignites the powder

TRUE

How do you pick up a gun retrieved from a crime scene?

By the edge of the trigger guard OR checkered portion of the grip so you don’t leave fingerprints

Protocol to collect a gun from a crime scene:

1. The weapons hammer and safety position should be recorded

2. Unload the weapon

3. mark for identification and a chain of custody must be established

• revolver = the chambers, their positions and corresponding cartridges must be recorded

Steps to collect bullets and bullet casings from a crime scene:

1. Record the location of all fired and unfired ammunition

2. scribe the investigator’s initials on the base or the nose of the bullets collected

3. wrap the bullets in tissue paper before placing the bullets each in separate boxes for shipment to the crime lab

Equipment used for ballistics?

Comparison Microscope

Rifiling

impressing a barrel’s inner surface with spiral grooves

Lands

the surfaces of the original bore that remain between the grooves after rifling

Grooves

what is being impressed into the barrel of a gun in a spiral design when putting a gun through the process of rifling

Caliber

the diameter of the gun barrel measured between opposite lands

Gauge

diameter of a shotgun barrel

Tool mark

any impression caused by a tool coming into contact with another object

T or F: Ejection hooks and extractors are seen in revolvers

FALSE: revolver bullets stay within the rotation chamber in the revolver

Ejection hook

the mechanism in a firearm that throws the cartridge case from the gun

Etractor

The mechanism in a firearm by which a carriage of a fired case is withdrawn from the firing chamber

Magazine clipping

the mechanism in a firing arm that holds the bullets

Breech block

stops the bottom of the bullet from going through the back of the gun

Methodology on how to collect and identify tool markings

• If the impression is on a readily recoverable item, the evidence is transported intact to the laboratory.

• If the surface cannot be submitted to the lab, the investigator may be able to preserve the print in a matter similar to lifting a fingerprint

NIBIN

produces databases files from bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms

Process used to get impression prints out of soft earth

Casings and Photography

Difference between handgun barrels and shotgun barrels

handgun barrels are rifled, shotgun barrels are smooth

Patterns of gunpowder residue if the shooter was ONE INCH away

• star-shaped (sttellate) tear pattern around the bullet hole entrance, surrounded by a rim of a smokeless deposit of vaporous lead

Patterns of gunpowder residue if the shooter was 12-18 INCHES away

• halo of vaporous smoke deposited around a bullet hole

Patterns of gunpowder residue if the shooter was 25 INCHES away

• scattered specks of unburned and partially burned powder grains without any accompanying soot

Patterns of gunpowder residue if the shooter was 3 FEET away

• will not depost any powder residue and the only visual is a dark ring around the hole (bullet wipe)

Name TWO firearm search systems

DRUGFIRE and IBIS

T or F: firing a weapon ONLY propels residues toward the target

FALSE; it also blows gunpowder and primer residues back towards the shooter

Examiners measure the amount of ___ and ____ on the relevant portion of the suspect’s hands

barium and antimony

What technique is useful in recovering latent dust prints on the floor?

Electrostatic lifting technique

What technology can visualize latent blood impressions?

Chemical enhancement