Chapter 8

Toolmarks and Firearms Chapter Objectives Toolmark – Definition Firearms Examination – Background Firearms Evidence Examination and Comparison Use of Firearms Evidence for Reconstruction Serial Number Restoration The Firearm and Toolmark Examiner Profession

I. Toolmark Definition A toolmark is a pattern resulting from a harder marking device (tool) being forced against a softer object Toolmarks are usually either striations (scratches) or impressions Striations result from a sliding action, whereas impressions are a result of forcing the tool into the surface

I. Toolmark Definition: Class & Individual Characteristics Toolmarks can have either class or individual characteristics and sometimes both The basic size and shape of the toolmark is a class characteristic and can tell something about the kind of tool that made the toolmark The individual characteristics are usually caused by stria

I. Toolmark Definition: Residue from Softer Object on Tool The tool should be first examined using a stereomicroscope for residue If the residue on the evidence tool is shown to be consistent with the surface that was scratched, the association of the tool with the surface is greatly strengthened Material characteristic of the tool may also be left in the toolmark

I. Toolmark Definition: Types of Toolmarks Three basic types: indented, striated, and a combination of the two Indented marks occur when the tool is pushed into the surface Striated marks occur when the tool slides across the surface Combination marks occur when the tool is pushed in and then slides across the surface

I. Toolmark Definition: Collection of Toolmarks A toolmark on a movable object should be protected and sent to the lab A toolmark on a fixed item, should be thoroughly photographed and then cast using silicone rubber A suspect tool should never be placed into the toolmark, as there is a potential to damage the mark and compromise the value of any residue on the tool surface

I. Toolmark Definition: Examination & Comparison of Toolmarks As trace evidence may be present either on the tool face or in the mark, it is important to collect control samples from an area near the mark The examiner then attempts to reproduce the toolmark by making test impressions in similar material The toolmark and test impressions are then examined using a comparison microscope

I. Toolmark Definition: Examination & Comparison of Toolmarks The examiner may conclude that: – The toolmark was made by that tool and no other tool – The marks are consistent in class characteristics and show a number of other similarities (the tool could have made the mark) – The marks are clearly different (disassociation) – The marks are not sufficiently clear (inconclusive)

I. Toolmark Definition: Examination & Comparison of Toolmarks To summarize, toolmark examinations may provide the following information: – What kind of tool was used to make a mark – The action which made the mark – The presence of residue consistent with the damaged surface – The particular tool that was responsible for the toolmark

II. Firearms Examination - Background A firearm is a device for accelerating a projectile to a high speed, sending it towards a selected target The energy that provides the driving force for the projectile is contained in the cartridge A cartridge consists of four basic components: the case, powder, projectile, and primer

II. Firearms Examination – Background Cartridge Components: the case – the container for the other three components the powder – small disks, cylinders, or balls of smokeless powder (cellulose nitrate) the projectile (bullet) – usually made from lead or copper-coated lead the primer – consists of a shock sensitive material

II. Firearms Examination – Background The “firing train” process: The firing pin strikes the primer “cup” located on the base of the case, compressing the cup and causing the shock sensitive primer to ignite The primer then transfers a spark or flame to the powder charge, located in the body of the case The burning powder rapidly gives off heat & gases and the pressure forces the projectile from the case and down the barrel of the weapon

II. Firearms Examination – Background Rifling: Rifling refers to the helical (spiral) grooves cut or impressed into the barrel of a handgun or rifle to cause the exiting projectile to spin The raised areas are known as “lands” and the depressed areas, “grooves” A spinning projectile has a flatter trajectory and flies a truer path to the target

II. Firearms Examination – Background Class Characteristics: The number of lands and grooves in a firearm barrel The widths of the lands & grooves The direction in which the lands and grooves spiral (the “twist”) can be either right or left The caliber, the distance between two opposing lands in hundreds of an inch (US) or in millimeters

II. Firearms Examination – Background Computer Databases: The FBI maintains a central computerized firearm file called the General Rifling Characteristic file (GRC) Firearm examiner can search the file with the caliber, number of lands and grooves, their widths, and direction of twist for the make and model of the firearm that could have fired the crime scene bullet

II. Firearms Examination – Background Individualizing Features: Imperfections in the lands during manufacture or caused by wear, nicks, scratches etc., will be mirrored on the surface of the fired bullets These rifling imperfections are unique to each barrel and form the basis for projectile-to-barrel identification

II. Firearms Examination – Background Types of Firearms Classification by firing mechanism: – Single shot - fire one round then require manual ejection of the cartridge casing before another round can be fired – Semiautomatics - fire one bullet then reload with a fresh cartridge each time the trigger is pulled and released – Automatics - continue to fire projectiles until the trigger is released

II. Firearms Examination – Background Types of Firearms Classification by design & purpose: 1. Rifles – A firearm designed to be fired from the shoulder and normally has a long barrel – Can be single shot, semi-automatic, or fully automatic

II. Firearms Examination – Background Types of Firearms Classification by design & purpose: 2. Handguns: – A firearm with a defined barrel length limit – Can be single shot, revolvers, or semi-automatic pistols – Revolvers are handguns that have a rotating cylindrical cartridge holder, allowing the weapon to be fired semi-automatically

II. Firearms Examination – Background Types of Firearms Semiautomatic Pistols are mechanically analogous to the semi-automatic rifles Cartridges are placed in a magazine, which is located in the grip of the firearm Empty cartridge cases are automatically ejected

II. Firearms Examination – Background Types of Firearms Classification by design & purpose: 3. Shotguns: – Designed to be fired from the shoulder, have long barrels, but are generally not rifled – Shotgun shells, contain either pellets or a slug packed into a cartridge along with the powder charge and primer

II. Firearms Examination – Background Collection & Preservation of Firearms Evidence A firearm must be rendered safe before collecting and packaging With revolvers, the cylinder position that is lined up with the barrel must be recorded Bullets and cases recovered from the scene must be carefully marked for identification or sealed in containers that are marked Firearm evidence should always be sent to the lab for analysis so that connections can be made to other cases using the firearm database

III. Firearms Evidence Examination & Comparison: Examination for Safety & Physical Condition Two key parts of the initial physical examination: – ensuring that no cartridges are left in the firearm – sighting down the barrel to verify that it is not obstructed The weapon is then “dry fired” (no cartridge) to ensure that all the different parts are working The basic class characteristics are noted along with make, model and serial number

III. Firearms Evidence Examination & Comparison: Functionality & Obtaining Control Bullets & Cases Firearms are test fired to determine functionality, proper working of the safety features, and to obtain known specimens Functionality is the ability of a firearm to fire a projectile when the trigger is pulled Two or three test firings are done into water-filled bullet recovery tanks

III. Firearms Evidence Examination & Comparison: Bullet & Cartridge or Shotshell Case Comparisons A comparison microscope is used for the examination of bullets and casings With bullets, fine striations on the interior of the land impressions are examined and compared The examiner looks for areas of agreement or disagreement between the stria of K specimens & the evidence

III. Firearms Evidence Examination & Comparison: Bullet & Cartridge or Shotshell Case Comparisons With cartridges, the firing pin impressions left by the firing pin on the primer cup portion of the cartridge can often be individualized to a particular firearm Cartridge cases can often be associated to a particular weapon by breech face markings left on primer cup

III. Firearms Evidence Examination & Comparison: Bullet & Cartridge or Shotshell Case Comparisons Cases recovered from semiautomatic weapons may have extractor &/or ejector marks that may provide enough information for individualization Shotshell cases can acquire firing pin impressions, breech face markings, and extractor &/or ejector marks Shotshells can be individualized to a shotgun analogous to cartridges from a handgun or rifle

III. Firearms Evidence Examination & Comparison: Firearm Databases NIBIN (National Integrated Ballistic Identification Network) contains images of bullets and cartridge cases recovered from scenes or test fired from seized weapons The database can connect different cases through bullet and cartridge case evidence

IV. Use of Firearms Evidence for Reconstruction Recovered Firearm & Fired Evidence in Reconstructions Trigger pull tests are frequently done with recovered firearms to evaluate the sensitivity of the trigger and evaluate the accidental discharge possibility Safety mechanisms are evaluated to test if the weapon would fire if accidentally dropped Bullets may have trace evidence that will provide information about the objects encountered during its travel

IV. Use of Firearms Evidence for Reconstruction Muzzle to Target Distance – Powder Pattern Muzzle to target distance estimates are based on the comparison of powder patterns produced at measured distances using the same firearm and ammunition Both the distance estimate and the determination of the projectile trajectory are important in the reconstruction of a shooting incident

IV. Use of Firearms Evidence for Reconstruction GSR on Hands – Dermal Nitrate, Lift, Swab, Tape Gun shot residue (GSR) refers to materials created by the firing of a firearm, particularly from the ignition of the primer The early dermal nitrate test (paraffin test) has been shown to be unreliable and prone to false positive results Analyzing swabs of the suspect’s hands for the presence of Pb, Ba & Sb, is limited by the rapid loss of particles, environmental contamination, and variable deposits by different firearms

IV. Use of Firearms Evidence for Reconstruction GSR on Hands – Dermal Nitrate, Lift, Swab, Tape The most reliable method for detecting GSR particles requires a Scanning electron microscope (SEM) with an energy dispersive X-ray analyzer (EDX) Samples collected using tape are examined by the SEM for particles with characteristic morphology (shape) Elemental analysis for the presence of Pb, Ba & Sb is conducted using the EDX

V. Serial Number Restoration The process used to impress the serial number in the metal, deforms the crystal structure underneath the stamped numbers making it susceptible to chemical attack The examiner first smoothes- out the damaged area then applies an acidic solution to slowly dissolve the metal The acid preferentially attacks the deformed regions revealing the original serial numbers

VI. The Firearms and Toolmark Examiner Profession The primary professional organization of firearms and toolmark examiners is the Association of Firearms and Toolmark Examiners (ATFE) A Scientific Working Group for Firearms and Toolmarks (SWGGUN) was recently established to examine and recommend standards of practice in the firearm and toolmark field