GSR
Gun shot residue
Gun Shot Residue
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Trace evidence may be found after a gun has
been fired.
During this combustion reaction, not all of the
material is fully used.
The excess material may be expelled from the
barrel, casing, or wherever the smoke and heat
escape.
The material may settle on the shooters hands,
clothing or hair and be found at the scene as
well.
GSR
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Chemicals are used to react with compounds
left by the ignition of the gun powder
Gun powder is made of nitrates
Metals (lead and barium) from the primer
may also be present
These chemicals are what make Gun Shot
Residue (GSR)
GSR
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You will be using two different chemicals that
react with the presence of the products of a
fired weapon.
Diphenylamine detects the presence of nitrates
Sodium rhodizonate detects the presence of
lead and barium
What you will do
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You will test GSR with the two chemicals
You will run a positive control using lead
nitrate
You will then test the unknown for GSR
The scenario
Two individuals were apprehended for the
robbery of a convenience store. The store
clerk was shot in the torso and later died at
the hospital.
No gun was found at the scene and
neither individual is taking the blame
for firing the gun.
A piece of sleeve, around the wrist
area, from each individual’s shirt has
been sent to you. Your job is to help
authorities determine if either had
anything to do with the shooting.
What to do
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Get a piece of notebook paper to record your
findings. You will be able to use this paper on
your ballistics test.
Your paper should include what makes up
GSR and what chemicals are used to detect
these chemicals.
You will also include the colors of a positive
and negative result using these chemicals.
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Make a chart showing the results of everything
you do.
Label everything clearly so you understand the
results of all your tests.
You will first do a positive control test on an
alcohol pad using lead nitrate.
Gun residue presumptive test
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Open the alcohol pad and put into a petri dish. Place
a drop of lead nitrate on two corners of the alcohol
swab
Place a drop of Diphenylamine on the drop of the
lead nitrate. Note that this chemical detects the
presence of nitrates from the gun powder
Place a drop of sodium rhodizonate on the other drop
of the lead nitrate. Note that this chemical detects the
presence of lead and barium from the primer.
Record color changes occurring with each chemical.
Expected results
Lead nitrate
Diphenylamine
sodium rhodizonate
blue
red
GSR test on the suspects
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Now you will test the presence of GSR on the sleeves
of the suspects.
The suspects are identified as suspect 1 and suspect 2.
Obtain a sample of each of one of the suspects
sleeves. DO NOT TOUCH WITH YOUR HANDS.
USE A CLEAN FORCEP.
Add a drop of each of the test chemicals
(Diphenylamine and sodium rhodizonate) and record
your results.
Repeat with the other suspect.
Expected results
Diphenylamine
sodium rhodizonate
Suspect 1
Pale yellow
Light yellow
Suspect 2
Dark blue
Dark red
Your conclusion
Remember, neither individual is
taking the blame for firing the gun.
Are they telling the truth??
Write your conclusion on your paper.