Firearms and Toolmarks Lecture PDF

FIREARMS AND TOOLMARKS BALLISTICS VS. FIREARMS IDENTIFICATION Ballistics is the study of projectiles in motion and is a branch of applied physics. Ballistics considers: Humidity Temperature Wind Projectile weight Projectile velocity Curvature of the earth Distance traveled BAL...

FIREARMS AND TOOLMARKS BALLISTICS VS. FIREARMS IDENTIFICATION Ballistics is the study of projectiles in motion and is a branch of applied physics. Ballistics considers: Humidity Temperature Wind Projectile weight Projectile velocity Curvature of the earth Distance traveled BALLISTICS VS. FIREARMS IDENTIFICATION Firearms Identification is a branch of forensic science that deals with the microscopic comparison of imperfections left by specific firearms on fired bullets and cartridge cases. The uniqueness of each firearm transfers to the cartridge case and bullet whenever the weapon is fired. This has been proven through physical sciences, including physics, metallurgy, metallography and materials science. INTRODUCTION Structural variations and irregularities caused by scratches, nicks, breaks, and wear may permit the analyst to relate: A bullet to a gun A scratch or abrasion mark to a single tool Cartridge cases from multiple crime scenes to each other Firearm and toolmark examination can individualize the evidence to a source.  REVOLVER PARTS Barrel Top Strap Hammer Cylinder Ejector Rod Release Cylinder Muzzle Crane Trigger Trigger Guard Frame Butt PISTOL PARTS RIFLE PARTS SHOTGUN PARTS HOW A GUN WORKS The Cycle of Fire Feeding Chambering Locking Firing Unlocking Extraction (pulling) Ejection (pushing) Cock FIRING A WEAPON 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. The expanding gases generated by the burning gunpowder propel the bullet forward through the barrel, simultaneously pushing the spent cartridge case or shell back with equal force against the breechblock. The cartridge case is marked by its contact with the metal surfaces of the weapon’s firing and loading mechanisms. HOW A GUN WORKS GENERAL RIFLING CHARACTERISTICS General rifling characteristics associated with firearms include: caliber (bore diameter) of the barrel grooved impressions inside a barrel conventional vs. polygonal number of land and grooves land and groove width dimensions direction of the twist of the rifling grooves GUN BARREL MARKINGS The gun barrel is produced from a solid bar of steel that has been hollowed out by drilling. The microscopic drill marks left on the barrel’s inner surface are randomly irregular and serve to impart a uniqueness to each barrel. GUN BARREL MARKINGS The surfaces of the original bore remaining between the grooves are called lands. The grooves serve to guide a fired bullet through the barrel, imparting a rapid spin to ensure accuracy. GUN BARREL MARKINGS The inner surface of the barrel of a gun leaves its markings on a bullet passing through it. Striations are impressed into the metal as the negatives of minute imperfections found on the rifling cutter’s surface, or they are produced by minute chips of steel pushed against the barrel’s inner surface by a moving broach cutter. These striations are particular to each gun and form the individual characteristics of the barrel. SHOTGUNS Unlike rifled firearms, a shotgun has a smooth barrel. Shotguns generally fire small lead balls or pellets that are not impressed with any characteristic markings that can be related back to the weapon. SHOTGUNS The diameter of the shotgun barrel is known as its gauge. The higher the gauge number, the smaller the barrel’s diameter. CALIBER The caliber of the rifle or handgun barrel is the diameter measured between opposite lands. Cross-section of a barrel with six grooves. The diameter of the bore is the caliber. CALIBER The term caliber generally refers to the diameter of the bullet being fired, but there are NO hard and fast rules when it comes to naming ammunition or weapon calibers. Standard calibers generally reflect the diameter of the bullet in hundredths of an inch, so 22 caliber is.22”, 50 caliber is.50”, etc. Metric calibers refer to the diameter of the bullet and the length of the assembled cartridge, e.g. 9x19mm 7.62x39mm. If the number is the same, but the caliber name has different words it usually means that the bullet diameters are the same, but the cartridge length or type of cartridge case are different. 22 Caliber Short 22 Caliber Long AMMUNITION Cartridges consist of four major components: 1. Case 2. Primer 3. Powder 4. Projectile(s) (Bullets, slugs, or shot) THE FIRED BULLET The lands and grooves of the rifled barrel engrave themselves onto the fired bullet. The examiner can determine many class characteristics of the firearm source: Bullet caliber, number of lands and grooves, their widths, and direction of twist. This information narrows down the list of possible firearm sources. FIREARMS ANALYSIS Firearm Examiners perform: Bullet, cartridge case, and shotshell comparisons Weapon operability Comparison of action marks Bullet trajectory determinations Serial number restoration Distance & shot pattern determination Toolmarks Miscellaneous Trigger Pull Determination Functioning of Safeties Magazine capacities Automatic / Semiautomatic CONDUCTING THE EXAM STEP #1 First, a thorough exam of the firearm is made to determine functionality, trigger pull, markings, features, etc. FUNCTIONALITY EXAM STEP 1 Information noted during a standard firearm routine: Manufacturer Model Caliber Serial Number Barrel Length GRC Type of Action Ammunition Capacity Safeties Trigger Pull Operating Condition Test Fire information Misc. information CONDUCTING THE EXAM STEP #2 The weapon is then test fired into a water tank and both the cases and bullets are recovered. CONDUCTING THE EXAM STEP #3 The cases and bullets are compared with a comparison microscope, two microscopes joined together by an optical bridge. COMPARISON MICROSCOPE Two bullets can be observed and compared simultaneously within the same field of view. The lands and grooves of the test and evidence bullets should have identical widths and the longitudinal striations on each must coincide. Even small fragments have enough detail for comparison  BULLET EXAMINATION No two rifled barrels, even those manufactured in succession, will have identical striation markings. The number of lands and grooves and their direction of twist are points of comparison during the initial stages of an examination between an evidence bullet and a test-fired bullet. Any differences in these class characteristics serve to eliminate the possibility that both bullets traveled through the same barrel. Check on Learning Main purpose of Rifling? Accuracy Number of lands and grooves always the same? True Which cartridge has the smallest bullet diameter? 22 Long Rifle, 7.62x99mm, 223 Remington, 9mm Luger, 50 BMG, 17 HMR (Answer: 7.62x99mm) Unique about comparison microscope? Can compare side to side bc of optical bridge, has 2 stages, has an oblique light source Label parts of a cartridge? CARTRIDGE CASES MARKS ON CARTRIDGE CASES Two Breech Face Marks Firing Pin Hole Breech Face Case on left was a Case on right was test fire in the lab. recovered at a crime scene. CARTRIDGE CASE COMPARISON The firing pin, breechblock, and ejector and extractor mechanism also offer a highly distinctive signature for individualization of cartridge cases. The shape of the firing pin will be impressed into the relatively soft metal of the primer on the cartridge case. The cartridge case is impressed with the surface markings of the breechblock. FIRING PIN IMPRESSIONS CARTRIDGE CASE COMPARISON Other distinctive markings that may appear on the case as a result of metal-to-metal contact are caused by the: Ejector, which is the mechanism in a firearm that throws the cartridge or fired case from the firearm. Extractor, which is the mechanism in a firearm by which a cartridge of a fired case is withdrawn from the firing chamber. Magazine or clip, which is the mechanism that in a firearm holds the bullets. EXTRACTOR The extractor is a device found on most firearms except revolvers, which helps pull the empty case out of the gun after it is fired. Extractors work by pulling on the edge of the cartridge rim and leave striated marks as shown below. Extractor Marks under the comparison microscope Extractor EJECTOR As the extractor pulls the case back, it strikes a hard protrusion or bump, called the ejector, which caused the case to fling out of the weapon. While the extractor pulls, the ejector pushes and usually leaves marks on the very edge of the cartridge case rim. Ejector Marks under the comparison microscope Ejector marks Ejector  “THE KAUFMAN DA MURDERS” Mark Hasse Longtime Dallas and Kaufman CO Prosecutor Private Pilot Killed in front of Kaufman CO Courthouse on January 31, 2013 while walking into work Initially suspected Cartels/Aryan Brotherhood Mike and Cynthia McLelland Elected District Attorney of Kaufman CO Both killed at home Easter weekend (April) 2013 38  SUSPECT – ERIC WILLIAMS Justice of the Peace in Kaufman CO Former Police Officer Member of Mensa Eccentric Convicted of stealing computer monitors from the county Owner of over 60 different firearms and 10,000 cartridges of various calibers https://www.nbcnews.com/dateline/video/vendetta-- part-9-499606595860 39  THE EVIDENCE Kaufman CO Courthouse Bullets recovered from scene and autopsy Same unknown firearm, 5 lands and grooves with right twist (Ruger, Smith & Wesson, and Taurus) McClelland residence All bullets fired from same firearm All cartridge cases from same firearm The storage unit None of the firearms identified to evidence from either crime scene, tested, over 20 different firearms One cartridge identified as having been cycled in same firearm as McClelland shootings Car seen by witnesses also recovered 40  EVIDENCE (CONT) The Bridge Cartridge cases linked to guns from storage unit The Lake Two revolvers recovered, one of which identified to Eric Williams by serial number Other revolver identified to bullets from Hasse autopsy 41 EMERGING TECHNOLOGIES Emerging technologies center on two different aspects: imaging and computer algorithms for comparison Imaging Techniques Confocal Microscopy Gel-Sight Laser scanning Detection Algorithms Congruent Matching Cells (NIST) IBIS/NIBIN CONFOCAL MICROSCOPY Uses a laser as a light source Can image along multiple focal planes Image is independent of any surface irregularities or reflectivity IMAGING ALGORITHMS Computers excel at detecting small variations in color. Difficulty is in recognizing what is part of a reproducible toolmark and what is random “noise”. NIST has introduced the congruent matching cells algorithm which has examiner input on areas of interest and areas of disinterest. Computers are able to differentiate 64 shades of gray; humans can only differentiate 16. Difficulties arise in accounting for damage, distortion, and manufacturing marks. Some technologies are currently in use, mostly as a verification tool, as well as the IBIS/NIBIN system. NIBIN NETWORK The National Integrated Ballistics Information Network (NIBIN) is a database of bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms, linking a specific weapon to a crime(s). The ultimate decision for making a final comparison will be determined by the forensic examiner through traditional microscopic methods. FIREARMS EVIDENCE COLLECTION Firearms collected at the crime scene are held by the edge of the trigger guard or by the checkered portions of the grip. Before the weapon is sent to the lab, all precautions are taken to prevent accidental discharge of a loaded weapon. It may be necessary to unload the weapon. When a revolver is recovered, the chambers, their positions, and corresponding cartridges are recorded. FIREARMS EVIDENCE COLLECTION Bullets recovered at the crime scene are scribed with the investigator’s initials, either on the base or the nose of the bullet. The obliteration of striation markings that may be present on the bullet must be avoided. Fired casings are identified by the investigator’s initials placed near the outside or inside mouth of the shell. Discharged shotgun shells are initialed on the paper or plastic tube remaining on the shell or on the metal nearest the mouth of the shell. GUNSHOT POWDER RESIDUE When a firearm is discharged, unburned and partially burned particles of gunpowder in addition to smoke are propelled out of the barrel along with the bullet toward the target. If the muzzle of the weapon is sufficiently close, these products will be deposited onto the target. Gunshot Powder Residue forms a pattern in a cone shape, like the beam of a flashlight. The distribution of gunpowder particles and other discharge residues around a bullet hole permits an assessment of the distance from which a handgun or rifle was fired. GUNSHOT POWDER RESIDUE Gunshot Powder Residue can be used to provide an estimate of how far away someone was at the time they were shot. The closer someone was at the time of discharge, the heavier and denser the pattern. The further someone is, the larger and more disperse the pattern. Gunshot Powder Residue is detected through a series of microscopic and chemical exams. Patterns on skin are estimated by medical examiners while patterns on clothing are analyzed by crime laboratories. Gunshot Powder Residue can be disturbed by handling, blood, medical intervention, the presence of an intervening object, specific firearm/ammunition used, and many other variables. DISTANCE DETERMINATION The distance from which a handgun or rifle has been fired is determined by a 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 from a target. By comparing the test and evidence patterns, the examiner may find enough similarity in shape and density upon which to base an opinion as to the distance from which the shot was fired. DISTANCE DETERMINATION In cases where the weapon is held in contact with or