706.3.6pp Firearms & Toolmarks F21.pdf

FOS 706 Physical & Biological Evidence Introduction ■ Why are firearms and toolmarks grouped together? ®Similarity in analysis of markings Firearms & Toolmarks PROFESSOR LINDA ROURKE 1 2 Introduction Types of Firearms ■ Rifles What is a firearm? ■ Pistols ■ Shotguns 3 4 Types of Firearm...

FOS 706 Physical & Biological Evidence Introduction ■ Why are firearms and toolmarks grouped together? ®Similarity in analysis of markings Firearms & Toolmarks PROFESSOR LINDA ROURKE 1 2 Introduction Types of Firearms ■ Rifles What is a firearm? ■ Pistols ■ Shotguns 3 4 Types of Firearms: Rifles ■ Long arms with a rifled barrel. ■ Consists of barrel, firing chamber, shoulder stock, provision for loading and unloading. ■ Single-shot, repeating or semiautomatic ■ Long barrel & more gunpowder provides high velocity, stability and range, greater accuracy. 5 6 1 Types of Firearms: Pistols FIREARMS: Rifling ■ Handguns Rifling and Rifled Barrels ■ Rifles & pistols ■ Lands (raised) and grooves (cut) on inside of metal tube ■ Imparts stability to bullet consisting of barrel, firing mechanism and handle. ■ Single-shot, revolver or semi-automatic. http://www.firearmsid.com/A_bulletIDrifling2.htm 7 8 Rifle and Pistol Calibers Rifle, Handgun, & Shotgun Bores Circles show bore sizes of common Caliber of weapon = diameter of barrel measured in hundredth or thousandth of an inch OR in millimeters are interchangeable. http://www.hunter-ed.com/sc/course/ch2_rifle_handgun_calibers.htm https://www.quora.com/How-does-forensics-match-a-bullet-to-a-weapon 9 cartridges. Having the same bore size does not mean different cartridges 10 Types of Firearms: Shotguns Semi-automatic Weapon ■ Uncut smooth-bore barrel lead pellets (shot) ■ measure of barrel diameter in terms of “gauge” = # lead balls of bore diameter which equals one pound ■ Use 11 12 2 Action Ammunition = the breech mechanism by which a firearm is loaded fired and unloaded ■ examples include: bolt action, lever action, hinged frame (break action), pump action, semi-automatic and full action bolt action lever action break action http://en.wikipedia.o http://www.neaca.co http://science.ho rg/wiki/Bolt_action m/GunRunnerSpecial wstuffworks.com s.html /shotgun5.htm Cartridges are the typical unit of ammunition ■ Holds together the following three components: – Projectiles – Propellant – Primer ■ pump action http://en.wikipedia.org/wiki/Pu mp_action 13 14 Ammunition: Projectiles ■ – ■ Ammunition: Propellant bullets - used in handguns and rifles ■ usually lead or lead core with copper jacket (harder metal) ■ pellets - used in shotgun cartridges Main explosive charge used to propel projectile from firearm. Packed in the body of the cartridge. Old fashioned black gunpowder: potassium nitrate, sulfur and charcoal. Modern smokeless powder ■ ■ – – 15 16 Ammunition: Primer ■ ■ ■ 17 single-base: nitrocellulose double-base: nitrocellulose and nitroglycerin Ammunition: Primer Initiating explosive used to detonate the propellant. Composed of impact sensitive percussion explosive. Main ingredients include lead, barium and antimony compounds although the recent trend is towards “cleaner” lead-free primers which use organic explosive materials. ■ ■ Centerfire: contained in primer cap at the base of the cartridge Rimfire: contained in rim at base of cartridge; typically for .22 caliber cartridges since diameter is too small for a primer cup 18 3 Forensic Firearms Evidence Firearms Evidence Analysis Collection And Preservation Of Firearms Evidence ■ Photo location of evidence. ■ Avoid contaminating fingerprint areas. ■ Mark cylinder for revolvers. ■ Label bullets & cartridge cases without destroying trace evidence or package separately in marked container. 19 ■ Microscopy : Transmitted or Reflected Light? ■ Comparison Microscope - with special mechanism for holding/rotating bullets and cartridge. 20 Bullet Comparisons Bullet Comparisons ■ Determine caliber, type, manufacturer ■ Direction and pitch of rifle twist ■ Diameter, length, weight & shape of bullet ■ Possible to individualize to the weapon from which it was fired. 21 ■ Examination – – – of striations the number and size of lands & grooves present. the actual pattern of striation markings will be unique to the firearm from which it was fired. striations should be analyzed by an experienced firearms examiner who will compare the unknown with an exemplar fired from the suspect firearm 22 Cartridge Case Comparisons ■ Determine caliber, type, manufacturer, often from the “headstamp”. ■ Individualizable to the weapon it was fired from. 23 24 4 Cartridge Case Comparisons Cartridge Case Comparisons ■ Breechface markings: come from the slamming of the base of casing against the breechface as the bullet exits the barrel. ■ Firing pin indentations: vary in size & shape. Firing pin marks on cartridges. Top, left to right: Spencer cartridge with a Ballard block type firing pin imprint; .50-70 cartridge struck with a Sharp's firing pin. Middle, left to right, Spencer cartridge struck twice; Spencer cartridge with a Jocelyn firing pin imprint. Bottom, left to right, Spencer cartridge struck by a Sharp's firing pin but fired in a Spencer; a standard Spencer firing pin. http://www.texasbeyondhistory.net/redriver/images/Firing-PinsBW.html 25 26 Computerized Firearms Evidence Analysis Cartridge Case Comparisons ■ For semi-automatic weapons the casing will also have extractor and ejector markings which come from the mechanism used to remove the casing when loading a new cartridge. 27 ■ Allows rapid cross comparison of bullets and casings from a database. ■ Can be used as an isolated unit or linked to interstate databases. 28 Computerized Firearms Evidence Analysis Early Computerized Firearms Evidence Analysis ■ Computerized databases are only for screening purposes. ■ The computer cannot determine if two casings/bullet came from the same gun. ■ It will narrow down the choices and an experienced firearms examiner can then obtain the actual samples to compare directly under a comparison microscope ■ DRUGFIRE: FBI system for casings and bullets ■ Integrated Ballistic Identification System (IBIS) developed by Forensic Technology, Inc. consists of a bullet comparison system (BULLETPROOF) and a casing comparison system (BRASSCATCHER) http://www.doj.state.wi.us/dle s/crimelabs/Firearms.asp 29 30 5 Current Computerized Firearms Evidence Analysis RECONSTRUCTIONS ■ NIBIN (National Integrated Ballistic Information Network): this is a database for both fired cartridge casing and bullet images – – Trajectory Determinations? ■ Use to identify position of the shooter ■ Aid in the recovery of projectiles. As an integrated system, can be used to compare evidence from regional and national databases Uses IBIS technology http://www.csigizmos.com/products/sceneaccessories/bullettrajectory.html http://www.adfs.state.al.us/NationalIntegrat edBallisticsInformationNetwork.htm 31 32 RECONSTRUCTIONS ■ Determining – – RECONSTRUCTIONS the Position of the Shooter: Methods of Determining Trajectory Patterns – ■ Use probes for short trajectories (metal rod or wooden dowel) ■ Use string for moderate trajectories (tan or gray string best for photographic purposes) (sags for extended trajectories) ■ Use laser for moderate to extended trajectories (requires fog/smoke to visualize well (rapid method) combine range determination and trajectory geometry determine both entry and exit holes carefully ■ Determining the Position of Movable Intermediate Targets: – requires having trajectory go through two or more fixed objects and knowing entry and exit holes. 33 34 RECONSTRUCTIONS RECONSTRUCTIONS Methods of Determining Trajectory Patterns – ■ These methods assume straight line trajectories: applicable for high velocity, moderate distant shots ■ Longer distance or low velocity have more of a parabolic arc trajectory 35 Methods of Determining Trajectory Patterns – ■ Not applicable for deflected shots ■ Examine markings and residues on bullets and compare to surfaces 36 6 RECONSTRUCTIONS RECONSTRUCTIONS Trajectory Analysis ■ Factors involved include: – – – Gunshot Residue Patterns: Distance Estimation ■ Assess claims of suicide, self-defense ■ Observe discharge residues around bullet hole for close-range shots; consider intermediary objects between firearm and final target. height and initial angle of firing type of firearm & ammunition energy lost in passing through surfaces; can limit angles of final trajectory. ■ Analysis: best to recover projectile(s) involved; compare witness story with evidence. 37 38 RECONSTRUCTIONS Muzzle-to-Target Distance Gunshot Residue Detection: ■ Muzzle-to-Target Distance: examine shape, size and distribution of the black sooty deposit on the target; can use chemical color/transfer tests to detect GSR patterns on dark/patterned targets. Distance Determination and Gunshot Residue Pattern 39 40 Muzzle-to-Target Distance ■ Detection – – – – Muzzle-to-Target Distance of lead ■ Detection Use sodium rhodizonate In acidic conditions, lead turns a magenta color Subsequent application of HCl turns the magenta to a bluish color Useful for transfer techniques – – – – 41 of nitrites Product of the detonation of the gunpowder Griess test uses sulfanilic acid to form a diazonium salt, which is then chemically converted to an azo dye Performed on desensitized photographic paper to give an orange color Used as a transfer technique 42 7 RECONSTRUCTIONS Gunshot Residue Detection: ■ Did the suspect recently shoot a gun? – – Use scanning electron microscopy and xray analysis. GSR can now be identified by a combination of morphology (spheroidal shape) and chemical composition (lead, barium and antimony from primer vaporization). 43 44 TOOLMARKS Types of Toolmarks ■ Result from contact between a tool and surface of object. ■ Can have class and individual characteristics. 45 ■ Indented (impression/compression marks) ■ Striated (sliding/scrape marks) ■ Combination 46 Collection of Toolmark Evidence Laboratory Comparisons of Toolmarks ■ Photography. Determine: ■ type of tool used ■ size of marking portion of tool ■ unusual features of tool ■ Package entire item if possible; otherwise remove portion of interest or make cast. ■ Do not try to match suspected tool to toolmark at the scene: compromises evidence, can cause damage. 47 ■ action which caused marks 48 8 Laboratory Comparisons of Toolmarks Did the suspect’s tool cause markings? ■ Best to examine original mark. ■ Compare to exemplar if suspect tool is found. ■ Use care in experimenting with the angle of use and portion used. ■ Time since use → additional wear 49 50 51 9