FSC239Y5 Lecture Notes - Lecture 24: Gunshot Residue, Scanning Electron Microscope, Statistical Hypothesis Testing
Lecture 24 January 12, 2017: Gunshot residue analysis
David Ruddell
• Cartridge components:
o Case
▪ Bullet
▪ Powder
▪ Primer (we are interested in this)
• Lead (Shock sensitive explosive)
• Barium (Oxidizer)
• Antimony (Fuel)
• What happens when you pull the trigger?
o Firing pun strikes the primer cup
o Primer is crushed, detonates
o Energy from primer sets of gunpowder
o Things go boom
o The heat causes the primer to vaporize
o Particles re-solidify quickly, deposits on shooter and nearby objects and
people (THESE PARTICLES ARE GUNSHOT RESIDUE. THE PRIMER)
• What is GSR?
o Particles that contains all three elements (Lead, barium, and antimony)
only a particle that has all three will be called GSR
o Spherical typically and about 1-10 micrometers
• “Primer discharge residue” or PDR is better to say but rarely used
• GSR kit
o 1 inch diameter aluminum tub covered with double sided tape
o 4 stubs are collected per suspect
o 2 from each hand
o Web and back of hand
• How is GSR detected?
o SEM/EDX (Scanning electron microscopy – energy dispersive x-ray
analysis)
o Automated analysis
o 24-48 hours to run handkit
o Instrument flags particles, but they need to be confirmed by a person
o It’s about 1/20 the width of a hair
o Typically find 5 or fewer particles on a handkit
o Cases involving garments are highly variable
• Positive result – meaning
o Fired a gun
o Near a gun when it fired
o Touched a surface with GSR on it
• Negative result- meaning
o Didn’t fire gun
o Gun didn’t deposit GSR on the hands
find more resources at oneclass.com
find more resources at oneclass.com
o GSR was lost due to activity
o Sampling was ineffective
• Limitations
o GSR cannot be used for firing angle, distance determination, or to
associate a specific gun or ammunition
o Total number of GSR particles varies greatly
o Victims are not sampled (gunshot residue travels with the bullet)
• What could look like GSR
o Pyrotechnic devices
▪ Fireworks don’t produce GSR
▪ They are different and can’t mimic GSR
o Airbags
▪ These DO produce GSR particles
▪ But they generally have an extra element in there that can
differentiate the two
• Studies – suicides
o Bexar county, TX
o Examined the hands of 112 people who had committed suicide using a
handgun
o 56 had no GSR on their hands
o Lack of GSR does not mean that somebody did not fire a gun
• Studies – bystanders
o Volunteers placed to the right, left, and behind shooter
o Gun is fired, hands sampled, stubs analyzed
o Positive for GSR in over 50% of the test firings
Chapter 8 Questions
• The distribution of gunpowder particles and other discharge residues around a
bullet hole permits and approximate determination of the distance from which the
gun was fired (True)
• Without the benefit of a weapon, an examiner can make an exact determination of
firing distance (False)
• A halo of vaporous lead (smoke) deposited around a bullet hole normally indicates a
discharge 12 to 18 inches from the target
• If a firearm has been fired more than 3 feet from a target, usually no residue is
deposited but a dark ring known as bullet wipe, is observed
• As a rule of thumb, the spread in the pattern made by a 12-gauge shotgun increases
1 inch for every yard of distance from the target
• An infrared photograph may help visualize gun powder deposits around a target
• One test method for locating powder residues involves transferring particles
embedded on target surface to chemically treated photographic paper (True)
• Current methods for identifying a shooter rely on the detection of primer residues on
the hands
• Determining whether an individual has fired a weapon is done by measuring the
elements barium and antimony present on the hands
find more resources at oneclass.com
find more resources at oneclass.com
