7. Firearms Investigation

7. Firearms Investigation Real/dp/B009GLVGNO"https://www.amazon.com/Pellet Firearms Investigation Firearms Examiners Can: • Match a bullet/casing to a gun. • Structural variations and irregularities caused by scratches; nicks and breaks. • Determine: • Firing Distance • Angle of Shot • Caliber of Weapon • Operability of Weapon Important Terms Rifling In A Barrel • Pistol: Barrel & Chamber in One Piece • Revolver: Rotating Cylinder • Rifle: Long Gun tIDrifling.htm"http://www.firearmsid • Shotgun: Shoots Many Small Pellets • Caliber: Diameter of Gun Barrel • Gauge: Diameter of Shotgun Barrel • Rifling: Process by Which Grooves/Lands Are Made • Grooves: A Depression In The Barrel • Lands: In Between Grooves • Striations: Microscopic Scratches Left In Barrel From Drill • Bullet: Expelled From Gun • Casing: Loaded Into Chamber Marks On Bullet • Lands & Grooves from the barrel will leave an impression on the fired bullet. • Right or left handed Land (A) and Groove (B) Impression on Bullet Integrated Ballistics Identification System (IBIS) • Images of projectiles and cartridge casings recovered from How a Gun Works When you pull the trigger, the crime scene or produced from evidence weapons are entered into hammer hits the back of the the database and searched. cartridge, causing a small • Links multiple crimes to a single weapon. explosion. The burning gunpowder • Potential hits are compared by an examiner on a comparison creates a lot of pressure, pushing microscope. the projectile forward. • Hits are not made by simply looking at the images in IBIS. The Precise Distance From Which A Firearm Has Been Fired Can Be Determined By: • Comparison of the powder residue pattern located on the victim’s clothing or skin against test patterns made when the suspect weapon is fired at varying distances. Wound Size • Exit wounds are usually much larger than entrance wounds. • Even without a bullet, entrance and exit wounds are easily identifiable. • Exit wounds may not exist (meaning the bullet is still inside the body). Abrasion Collar • Abraded area of tissue surrounding the entrance wound created by a bullet when it dents and passes through the skin. • Varies with angle of impact. Close Range Gunshot Wound • Possible to have blood spatter and shooting on the hand of the person firing the weapon. forensic Kinetic Energy KE = 1/2 mv2 Primer Residue Left On Hand • Powder Residue is left from the barrel of the gun and cylinder. • Muzzle Flash: Flame from the end of the barrel. • Collection of Firearm Evidence • Rubber coated or taped tools • Remove moldings (if necessary) • Mark bullets only on nose or base • Record serial numbers of guns • Mark all moving & removable parts • Unload loaded weapons • Mark cylinder hammer position (revolvers) Bullet Proof Vests Kevlar: Very strong & light fabric. • Do not clean Absorbs energy of bullet. • Remove moisture by cleaning (note in record) • If found in water, keep in water • Box for transport Primer • All ammo of suspect should be seized. Handguns & Rifles • Handguns fire bullets slightly lighter than rifles. • Shorter barrels with smaller explosive charges. • 700 to 1300 ft/s • Rifles have longer barrels and greater charge • 1500 to 3000 ft/s Chemical responsible for initiating combustion Barium, Antimony, Lead