mock trial

firearms identification

a discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon

ballistics

study of a projectile in motion

grooves

the cut or low-lying portions between the lands in a rifled bore

rifling

the spiral grooves formed in the bore of a firearm barrel that impart spin to the projectile when it is fired

bore

the interior of a firearm barrel

lands

the raised portion between the grooves in a rifled bore

caliber

the diameter of the bore of a rifled firearm; the caliber is usually expressed in hundreths of an inch or millimeters—for example, .22 caliber and 9 mm

gauge

size designation of a shotgun, originally the number of lead balls with the same diameter as the barrel that would make a pound; for example, a 12-gauge shotgun would have a bore diameter of a lead ball 1/12 pound in weight; the only exception is the .410 shotgun, in which bore size is 0.41 inch

breechface

the rear part of a firearm barrel

extractor

the mechanism in a firearm by which a cartridge of a fired case is withdrawn from the chamber

ejector

the mechanism in a firearm that throws the cartridge or fired case from the firearm

nibin

national integrated ballistics information network

ibis

integrated ballistics identification system

distance determination

the process of determining the distance between the firearm and a target, usually based on the distribution of powder patterns or the spread of a shot pattern

choke

an interior constriction placed at or near the muzzle end of a shotgun’s barrel to control shot dispersion

greiss test

a chemical test used to develop patterns of gunpowder residues around bullet holes

who is tbi accredited by?

ansi nab

ansi nab

american national standards institute national accreditation boardwh

what is accreditation?

certification obtained by laboratories from standardization organizations that recognize the laboratory's competence in performing specific tasks and ensure it produces accurate and reliable results.

what are class characteristics?

pre-determined features designed into a weapon before being manufactured that are shared by a specific group or model of weapon

ex: number of lands and grooves, width of lands and grooves, twist direction, caliber or bore diameter

what are individual characteristics?

unique microscopic markings left on projectiles or casings that are a result of random imperfections, tool wear during manufacturing, subsequent use, abuse or corrosion

what piece of equipment do you use to do comparisons?

comparison microscope

what is a comparison microscope?

is two distinct microscopes that are connected together by a specialized optical bridge that utilizes mirrors and prisms in order to let me visually examine two evidentiary items simultaneously through a single eyepiece set

what is rifling and where is it found?

is the spiral grooves formed in the bore of a firearm barrel that impart spin to a projectile when it is fired; exclusively located inside the bore

what are land and groove impressions?

land impressions are depressed areas and groove impressions are raised areas on a projectile

what is a cartridge?

is a self-contained unit of pre-assembled firearm ammunition that combines all the components need to fire a projectile in a single package

what are the four components of a cartridge?

• projectile/bullet

• case/casing

• propellant/gunpowder

• primer

projectile/bullet

solid metal piece sitting at the tip of the cartridge that exits the barrel and travels toward a target

case/casing

metal container that holds all the components together

propellant/gunpowder

chemical fuel packed inside; when ignited, burns rapidly and creates a large volume of expanding gas that forces a bullet forward

primer

small, impact-sensitive explosive charge at the base of the cartridge; when the firing pin strikes the primer, it sparks and ignites the main gunpowder charge

can you tell when a firearm was fired?

analyzing physical evidence, GSR patterns, gunpowder odor, barrel temperature, chemical changes inside the barrel

where are you employed

tennessee bureau of investigation’s nashville crime laboratory

what is your job title?

firearms and toolmark identification examiner

how long have you been working at tbi

since august 2022

what are the minimum qualifications for a forensic scientist at tbi?

• four year bachelors degree in science, forensic science or a related field

• minimum 20 credit hours in chemistry

• pass a background check

what is your educational background?

bachelors in science, in forensic science from middle tennessee state university

describe your training program with the tbi crime lab?

underwent courses learning the history and operability of firearms, how to properly examine firearms and projectile or other related items, and how to utilize international networks such as nibin and ibis and brasstax and matchpoint and completed supplementary courses through nfea

how long was your training period?

1 and ½ years

how is evidence received into the lab?

evidence is sent to our lab once processed at the evidence receiving unit

who can submit evidence?

law enforcement agencies, medical examiners, district attorneys

what is chain of custody?

is a permanent physical and electronic record that tracks the possession, movement, and integrity of evidence from the moment it is received to the agency until it is analyzed by the crime laboratory and returned to the submitting law enforcement agency or other authorized official

what occurs once evidence technicians have the evidence?

• begins documentation and intake paperwork (time and date log, packaging inventory, contents not verified stamp)

• digital entry into lims (laboratory information management system)

• barcoding and unique identification is added (lab case number and barcode to scan its movement)

• secure evidence in vault (once barcoded and logged, evidence is safely secured in the primary evidence vault)

• distributes to forensic scientist once a scientist has been assigned to the case (tech obtains evidence from vault and scans barcode to electronically transfer to the specific lab unit)

who has access to the evidence vault?

authorized personnel in the evidence receiving unit (supervisors)

how is evidence stored in the lab?

• before storage, all firearms must be completely unloaded and separate from ammunition to eliminate safety risk

• kept properly sealed or a temporary seal if there is a pause on an active examination

• evidence is stored in personal storage location for a specific scientist or unit bulk storage locations for larger or heavy firearms

• all internal movement in the lab is electronically tracked (physical location from lab bench to storage)

what is evidence?

any physical object, digital media or biological matter that is collected, submitted and analyzed to determine whether a crime occurred and to link a suspect or victim to a specific incident

when was the evidence received? from who and where

12-2-2024 at 2:30 pm from detective meredith grey of the lebanon police department

what is evidence receiving standard operating procedure?

evidence receiving unit receives it then submits it to the lab

did you notate the appearance of the evidence? was it sealed?

i did notate the appearance of the evidence, it was properly secured by zipties in a cardboard box and paper envelopes for the cartridge and bullet

what is quality control?

is a failure detection system used to measure, test, and verify that actual laboratory techniques and results are accurate, reliable and legally valid

what is quality assurance?

is a comprehensive system wide framework that is designed to prevent errors and guarantee that all laboratory operations meet strict scientific and legal standards

what are tbi’s quality control measures, if any?

mandatory control samples, equipment performance and safety checks, reagent and chemical verification, direct case reviews and verifications by a technical peer and administrator, performance tracking through proficiency tests and instrument calibration logs

do you perform proficiency tests? what are they and did you pass?

tbi has external and internal proficiency tests (ex: outside forensic agencies given blind and in: in house with real cases) and simulated mock case and trial testimony. firarms units is given a proficiency test yearly covering main disciplines (firearms and toolmark examinations and additional tests in nibin (ballsitics imaging), serial number restoration and distance determination

how many times have you testified in court, if any?

three times in tennessee state court

what are proper operating conditions for a firearm?

a firearms mechanical state allowing it to complete all the things it was designed to complete a firearm to cycle, lock, ignite and extract safely and reliably according to its design parameters

what were the results of your examination

test fired cartridge was compared to recovered cartridge 002 from firearm 001 and shared class characteristics of an elliptical firing pin impression, parallel and horizontal striations of breechface markgs, broad rectangular ejector marks, and claw engagement scratches from the extractor while the bullet was unsuitable for examination given it was heavily fragmented

what are the steps of a fire cycle?

1. feeding

2. chambering

3. locking

4. firing

5. obturation

6. unlocking

7. extraction

8. ejection

9. cocking

feeding

insertion of cartridges into a chamber and the breech bolt pushes the cartridge into final positon

chambering

insertion of the cartridge into the chamber

locking

breech bolt mechanism locks cartridge into position in barrel before firing

firing

when breech is fully locked, a pull on the trigger mechanically translates to the fiting pin release; in a cocked position, the firing pin has a hammer behind it with a spring that forces it toward the primer that is retrained only by a sear that is engaged by the trigger and pulling the trigger trips the sear from the engaging notch in the hammer which gets actuated by a cocked spring that drives the firing pin sharply against the percussion sensitive primer which fires the cartridge

obturation

occurs when powder gases under high pressure are sealed to prevent them from jetting between primer cup and cartridge case, cartridge case and primer wall, and projectile and bore

unlocking

reverse of the locking process and is frequently performed in conjunction with extraction

extraction

all cartridge cases are designed wtih a rim or groove at the base so that an extractor claw can grasp this edge in order to achieve extraction

ejection

at the final extraction stages, the cartridge case encounters a projection that is usually at right angles to the exit portal of the breech, rotating on the extractor fulcrum has the case base in contact with the opposite side by the ejector that flips the case out of the actuating mechanism

cocking

the hammer spring is usually cocked when the bolt of a rifle, pistol or repeated shotgun is retracted

what are the four atfe range of conclusions?

1. identification

2. inconclusive

3. elimination

4. unsuitable

identification

agreement of a combination of individual characteristics and all discernable class characteristics where the extend of agreement exceeds that which can occur in the comparison of toolmarks made by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool

inconclusive

• some agreement of individual characteristics and all discernible class characteristics but insufficient for identification

• agreement of all discernible class characteristics without agreement or disagreement of individual characteristics to an absence, insufficiency, or lack of reproducibility

  • agreement for all discernable class characteristics and disagreement of individual characteristics but insufficient for an elimination

elimination

significant disagreement of discernable class characteristics and or individual characteristics

unsuitable

for fired and mutilated cartridge cases and shotshell cases that do not bear microscopic marks of value for comparison purposes

what is an elliptical firing pin impression

oval shaped indentation left on the primer cup of a fired cartridge casing found in glocks

what are parallel and horizontal striation breechface marks?

microscopic manufacturing scratches left on the breechface stamped directly onto the primer and base of a cartridge casing when a bullet is fired

what are broad rectangular ejector marks

when a firearm has a wide, flat, rectangular ejector, it leaves a matching broad rectangular stamp on the cartridge’s base

what are claw engagement marks from extractor marks

distinct microscopic scratches/indentations left on the rim and groove of a cartridge casing by the extractor as it is spring loaded and hooked shaped that is attached to the slide or bolt carrier with the primary job to grip the rim of the cartridge casing and pull it backward out of the chamber after a round is fired so that the gun can cycle

what date did you issue your crime lab report

12-5-2024

what is the laboratory case #

#CL-2024867

what is the agency case #

#2024-530900