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EXAM #1 - CRIM 113 > Firearm and Toolmark Evidence > Flashcards

Firearm and Toolmark Evidence Flashcards

1
Q
  • Four universal firearm safety rules
A

o Treat all firearms as if they are loaded
o Never point the muzzle at anything you do not intend to destroy
o Never put your finger on the trigger until ready to fire
o Know your backstop

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2
Q

what happens when two objects interact?

A
  • When two objects interact with each other the harder object will leave marks on the softer object. The harder object is the Tool
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3
Q
  • Tool working surface =
A

the area of the tool that contacts the softer object to leave its mark

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4
Q
  • Class characteristics
A

measurable features of a specimen which indicate a restricted group source. They result from design factors, and are therefore determined prior to manufacture

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5
Q
  • Individual characteristics =
A

Marks produced by the random imperfections or irregularities of tool surfaces. These random imperfections or irregularities are produced incidental to manufacture and/or caused by use, corrosion, or damage. They are unique to that tool and distinguish it from other tools with the same class characteristics

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6
Q
  • Subclass characteristics
A

More restrictive group source than class characteristics that is also produced incidental to manufacturing. Characteristics that appear individual; however, they arise as carryover in the manufacturing process

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7
Q
  • Tool marks can be impressed marks or striated marks
A

o Impressed marks are marks produced when a tool is placed against another object and enough force is applied to the tool so that it leaves an impression
o Striated marks are marks produced when a tool is placed against another object and with pressure applied, the tool is moved across the object producing a striated mark

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8
Q

can impressed marks and striated have individual characteristics?

A

Impressed marks and striated marks may have individual characteristics, especially if the tool used is worn or damaged

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9
Q
  • Tool mark analysis?
A

o Need to establish the physical action necessary to make the questioned mark
o Using the tool, reproduce the mark in a softer material such as lead
o Compare the question mark with the known mark using a comparison microscope

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10
Q
  • Comparison microscope
A

o Allows for a bullet, cartridge case, and other toolmark comparisons
o Two separate stages
o Images side by side in microscope eyepiece
o Usually has a trinocular for a camera mount

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11
Q
  • Rifling
A

o The inner surface of the barrel is cut or impressed with spiral grooves
o Lands are the raised areas
o The rifling grooves engage the bullet and impart spin
o The spin stabilizes the bullet in flight

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12
Q
  • Gun barrel class characteristics
A

o Direction of twist (left or right)
o Land width (measured in thousandths of an inch)
o Groove width (measured in thousandths of an inch)
o Number of lands and grooves
o Caliber (measure of distance in inches from land to opposite land)

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13
Q
  • Gun barrel individual characteristics
A

o Striations within the lands and grooves
o Land impressions are the most individual
o No two rifled barrels will have identical striated markings

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14
Q
  • Bullet comparisons
A

o Gun barrel marks a bullet as it travels down barrel
o Markings constitute class and individual characteristics
o Result: bullet can be associated to a particular firearm

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15
Q
  • Caliber
A

o Firearms=The diameter of the barrel measured between two opposite lands
o Bullets=The diameter of the base of the bullet
o Three caliber naming conventions
* True caliber=actual measurement
* Nominal caliber=caliber family (e.g. nominal 38 caliber includes 9mm, 357 mag, 38 special, 380 Auto) Nominal caliber is not an actual measurement as in true caliber
* Cartridge designation=Manufacturers description of the cartridge and can be synonymous with nominal caliber

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16
Q
  • Cartridge cases and cycle of fire
A

o Firing pin strikes primer
o Primer ignites powder charge
o Gases are evolved
o Bullet is forced down the barrel
o Cartridge case obturates
o For auto and semi-autos the cartridge case is extracted and ejected and another cartridge is fed into the chamber

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17
Q
  • Source of markings found on cartridge cases
A

o Firing pin
o Firing pin aperture
o Breachface
o Chamber wall
o Ejection port
o Magazine lip
o Extractor
o Ejector

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18
Q
  • Shotguns
A

o Have smooth bore (no rifling)
o The wad can reveal the gauge and manufacturer of the ammo
o The smaller the gauge number the larger the bore diameter

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19
Q
  • Microscopic comparisons
A

o Identifications can be made when all class characteristics and a sufficient amount of individual characteristics agree with each other
o Eliminations can be made when one or more class characteristics don’t agree with each other and/or an insufficient amount of individual characteristics agree with each other
o Inconclusive is made when all class characteristics agree with each other, but an insufficient amount of individual characteristics agree with each other
o Unsuitable result is due to post-fire abrasions that destroy microscopic detail or fragment that does not contain any microscopic detail (rifling)

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20
Q
  • General rifling characteristics (GRC) database
A

o Maintained and updated by the FBI
o Caliber information
o Number of lands and grooves
o Direction of twist
o Land and groove widths
o Firing pin shape
o Type of rifling

21
Q
  • Partially burned and unburned gun powder contains:
A

o Lead
o Nitrites
* Lead and Nitrites are main two components for distance determinations
o Antimony
o Barium
o Others

22
Q
  • Contact Wounds
A

o Stellate pattern/ firearm imprint
o Little or no powder residue around wound
o Charring or melting of fabric on clothing

23
Q
  • Greater than Contact Wounds
A

o Partially burnt powder deposits around wound
o Powder density pattern will indicate distance

24
Q
  • Gun Shot Residue (GSR) testing
A

o Sodium Rhodizinate = test for lead
o Greiss test = test for nitrites (partially burnt gun powder)
o Greiss test must be done before Sodium Rhodizinate test (chemical interference)

25
Q
  • Visualizing GSRs
A
  • Visualizing GSRso Greiss test for Nitrites
  • Has to be done before NaRhodizonate
  • Reaction with nitrites gives orange color
    o Sodium Rhodizonate test for lead
  • Reaction with lead gives pink color
  • Lead verified by addition of hydrochloric acid (HCl) giving a violet color
26
Q
  • Distance Determination (Shotguns)
A

o Spread of shot pattern considered
o Choke: a constriction in the barrel to control the dispersion of shot
* Cylinder (no choke)
* Improved cylinder (1/4 choke)
* Modified (1/2 choke)
* Improved modified (3/4 choke)
* Full choke

27
Q
  • Distance Determinations
A

o Need the suspect weapon
o Need the suspect ammunition or the same type and if possible lot # of ammunition
o Need similar or same testing material (i.e. cotton, polyester, etc…)
o Need to know the circumstances surrounding the shooting (Indoors/Outdoors etc.)

28
Q
  • Gun Control Act of 1968
A

o Signed into law by President Lyndon B. Johnson on October 22, 1968
o Primary focus is the regulation of interstate commerce in firearms
o Requires serial numbers to be stamped or cast on the frame or receiver of a firearm

29
Q
  • Serial Number Restorations (Properties of Metals)
A

o Metals are polycrystalline in structure consisting of irregular shaped crystals or grains
o Interlocking regions between grains are grain boundaries
* Small grains=greater strength and toughness
* Large grains=greater ductility
o Elastic Deformation vs. Plastic Deformation
o Serial numbers are produced by stamping or laser etching (No restoration on laser etched numbers)
* Pin stamping, dot matrix, roll stamping, full number stamp
o Stamping is a cold-working process that compresses the grains and causes plastic deformation
o The plastic deformation region

30
Q
  • Serial Number Restorations
A

o Serial numbers are produced by stamping
o Stamping causes plastic deformation in the metal’s crystal structure
o This strain extends a short distance beneath the serial number
o Laser etched serial numbers cannot be restored
o Obliterated serial number
* Usually done by punching, grinding, filing, overstamping or overpunching, welding and other heating processes, drilling, and reapplication of original finish
* Can be done in combination

31
Q
  • Restoration Process
A

o Clean the surface
o Polish the surface
o Apply an appropriate etching agent
o The plastic deformed region dissolves faster than the surrounding metal
o Neutralize the etching agent
* Stops chemical reaction of etchant and metal

32
Q
  • Visualizing the serial number
A

o The plastic deformation region exhibits diffuse reflection while the non-deformed region exhibits specular reflection

33
Q
  • Evidence Collection (Firearms)
A

o Safety first
o Never stick anything in the barrel
o Pick up weapon by the knurled or checkered surfaces
o Unload the firearm
o Account for the ammunition in the firearm
o NEVER engage the firearm’s safety!! (it might discharge the firearm)
o Secure firearms in a box if possible

34
Q
  • Evidence Collection (Firearms-Double Action Revolvers)
A

o Mark cylinder location
o Note direction of cylinder rotation
o De-cock hammer (if necessary)
o Number cartridges and cartridge cases in relation to hammer location
o Secure in box if possible

35
Q
  • Evidence Collection (Firearms-Single Action Revolvers)
A

o Mark cylinder location
o Note direction of cylinder rotation
o De-cock hammer (if necessary)
o Free the cylinder to rotate
* Hammer down and loading gate open or,
* Hammer at half-cock and loading gate open
o Secure hammer for transport

36
Q
  • Evidence Collection (Firearms-Pistols)
A

o Drop magazine into bag or envelope
o Cycle action (pull slide back) and collect cartridge or cartridge case
o Check chamber
o Secure slide open for transport
o Secure pistol in box if possible

37
Q
  • Evidence Collection (Shotguns-pump action)
A

o Pull forend to open action
o Open bolt to eject shotshell
o Remove next shotshell from chamber area
o Close bolt 1/3 of the way, clear lifter, and unload magazine
o Look for the follower

38
Q
  • Evidence Collection (Rifles-semi and full auto)
A

o Remove or open magazine
o Pull bolt to rear to eject cartridge from chamber
o Transport with action open

39
Q
  • Evidence Collection (Rifles-lever action)
A

o Using lever, open action to eject cartridge
o Close action ~ 1/2 way to free next cartridge
o Remove loose cartridge
o Close action and repeat process until empty
o Look for the follower
o Transport with action open

40
Q
  • Evidence Collection (Rifles-bolt action)
A

o Using bolt handle, open action to eject cartridge from chamber
o Slide cartridges from magazine and remove
o Repeat above step until magazine empty
o Look for the follower
o Transport with action open (remove bolt if possible)

41
Q
  • Evidence Collection (Muzzle loaders)
A

o Remove any percussion caps from nipples
o Use the ramrod or dowel rod to check for loaded ball powder charge
o Percussion revolvers, look through nipples of each chamber (if dark, may be loaded)
o Transport so the firearm cannot discharge

42
Q
  • Evidence Collection (Bullets)
A

o If cloves become soiled (blood etc.) change gloves
o If removing from an object, leave encased in object and collect object if possible
o Wrap bullets in tissue and place in an individual box or coin envelope

43
Q
  • Evidence Collection (Cartridge cases)
A

o Remember: note ejected cartridge cases but ejection pattern interpretation is unreliable
o Pick up from mouth of cartridge cases
o Wrap in tissue and place in an individual box or coin envelope

44
Q
  • Evidence Collection (Clothing with GSR)
A

o Air dry if wet before packaging
o Try to collect clothing from victim before transport to Coroner’s office
o Fold carefully to protect bullet hole and surrounding area
o Wrap in paper and place in paper bag

45
Q
  • Evidence Collection (General Tool Marks)
A

o Photograph tool mark using oblique lighting at different sides of tool mark
o If possible, collect object containing the tool mark
o If appropriate, cast tool mark
o NEVER place suspect tool in question tool mark

46
Q
  • Evidence Collection (General Tools)
A

o Document tool type and location of tool working surface
o NEVER place suspect tool in question tool mark

47
Q
  • Evidence Collection (Shoe Impressions)
A

o Photograph with oblique lighting
o Collect the object the impression is in
o Chemically or physically enhance impression (Wet source)
o Impression lifting techniques similar to finger print lifting
o Electrostatic Dust Print Lifting (Dry source)
o Casting with dental stone if impression is in soil

48
Q
  • Evidence Collection (Tire Track Impressions)
A

o Photograph with oblique lighting
o Cast 3-foot length of tire impression
o Use Dental Stone when impression is in soil

49
Q
  • Labeling Evidence Containers
A

o Case number
o Collector name/identifier
o Agency name
o Date
o Item description
o Item number
o Item location

EXAM #1 - CRIM 113 (3 decks)

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