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Unit 4 Assignment B - Analysis of Forensic Evidence (Chemical)
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Analysing Forensic EvidenceUnit 4
Assignment B
Within this assignment, analytical techniques undertaken by forensic scientists and their
reliability and accuracy will be discussed and evaluated based on evidence collected from a
mock crime scene. Analytical techniques are used to determine facts surrounding a crime,
and find out what actually happened. A variety of physical, biological and chemical evidence
is used to do this. This report will discuss two chemical pieces of evidence from a crime
scene and justify why the method was used, as well as disadvantages and advantages of
the methods, and the validity of the results obtained.
Chemical Evidence
Chemical analysis is a vital piece of evidence within a crime scene investigation, this is
because it can determine cause of death (whether by drugs etc.) it can also involve looking
at gunshot residue, it is found commonly on most crime scenes, therefore analysing it can
link events at a scene.
Gunshot residue analysis
Immediately after a gun has been fired, gunshot residue, and this residue can then be
attached to people, or other things like furniture, toys etc. Within a gun, a compound called
Primer is used, this allows for the gunpowder within a gun to be set off. Primer has multiple
compounds within it, such as lead styphnate, antimony sulphide and barium nitrate. These
compounds are propelled back at the firer of the gun, and can get onto close surroundings.
Forensically analysing gunshot analysis involves extracting the metal found from the primer
and analysing it microscopically, using a scanning electron microscope. It is the analysis of
distinctive particles that are released from the firing of a gun - either onto skin or objects.
This is useful as it can provide evidence for things such as whether guns have been present
on a scene and fired, what location it was fired in, or even if vehicles have been used as
getaway cars. However, it may be expensive to use the equipment, and you need
specialised training. The equipment used is also not easily transportable - therefore you
can’t use it on a scene and it must be taken to the labs for analysis. This is also the only
method of analysing gunshot powder - therefore any limitations cannot be remedied with
further testing.
Gunshot powder can be lifted with adhesive tape - this is suitable for a scanning electron
microscope, swabs can also be used. Tape can be used to collect these samples off of skin
etc, this is useful as it provides a reliable collection method. However, make sure the tape is
clean and void of fingerprints, this can be done by wearing gloves, swabbing can also be
used on wet surfaces. Use the adhesive tape until it has lost its stickiness - this means the
sample is successfully collected.
Drug Analysis
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