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WJEC Criminology Unit 3 AC1.3
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WJEC Criminology Unit 3 - Crime scene to courtroom AC1.3 - Explain how evidence is processed
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Criminology Unit 3 AC1.3Explain how evidence is processed
, Criminology Unit 3 AC1.3
Explain how evidence is processed
Types of Evidence
- Two types of evidence: physical and testimonial
- Physical evidence is actual material or tangible articles such as DNA from blood or bodily fluids, or a physical
object like photographs or a weapon.
- Physical evidence uses Locard's exchange principle (created by a 1900s forensic scientist called
Edmond Locard)
- Locard’s exchange principle believed that “every contact leaves a trace” which means that a perpetrator
to a crime will bring something to the crime scene and will also leave with something
- SOCO’s work on this principle that physical evidence is left behind at every scene.
- An outdoor crime scene is the most vulnerable to loss or contamination of evidence. Individuals
with access to a crime scene can potentially alter, destroy or contaminate evidence . Greatest
risk is when officers fail to secure the crime scene properly alongside weather conditions which
can destroy or ruin evidence.
- Paul Kirk 1953 expressed the principle as “Wherever he steps, whatever he touches, whatever
he leaves, even unconsciously, will serve as a silent witness against him”
- Testimonial evidence is often spoken or written statements by witnesses, experts, victims or defendant.
- Evidence goes through a process of
- Collection - Transfer - Storage
- Analysis - Personnel
Collecting transferring and storing physical evidence
- Physical evidence needs to be collected, transferred and stored in order to preserve them and to prevent
contamination.
- Most contamination occurs when items are handled without gloves or by breathing, sneezing or coughing over
them.
- For serious crimes investigators wear protective clothing when they are collecting materials to avoid
contamination and protect themselves from hazardous substances.
- It includes a mask, hooded ‘scene suit’, overshoes and two pairs of gloves.
- For less serious crimes they wear only a mask and gloves.
Physical Evidence and how it needs to be stored
Bodily Fluids/ tissues (potential DNA evidence)
- Bodily fluids such as semen, blood and saliva and tissue such as skin flakes and hair can provide
important identification evidence because DNA can be extracted from them and compared with control
samples from the suspect to see if there is a match which would place the suspect at the scene.
- Blood Stains
- Before being collected must be allowed to dry naturally and left completely untouched
- Then be collected in a sterile way using gloves/ wearing a mask and sterilised tools
- Then packaged safely in an airtight, sterile container, labelled and sealed
- Then taken to a laboratory for analysis within 24 hours of being found
- Forensic scientists will check the DNA from the samples against other DNA samples in a
database with hopes of finding an exact or close match.
- Semen Stains
- Can be found on bedding or clothing and should be left to dry naturally
- The material with the stains should be placed into a paper bag inside a polythene bag
- If there are known victims of sexual assault then they should be examined by a doctor as
soon as possible
- Forensic scientists will check the DNA from the samples against other DNA samples in a
database with hopes of finding an exact or close match.
- Skin Flakes
- Are constantly shedding by us so can be found at a crime scene and analysed for DNA.
- Hair Samples
- Likely to be on clothing and if so the clothing should be wrapped in paper or placed in a
paper bag, sealed, labelled and sent to the forensic lab for examination.
- Any hair fragments found on furniture should be placed in paper,then marked and sealed.
- DNA is extracted from cells in the root to identify suspects or victims.
- Sometimes examinations of hair can reveal the possible race of the individual and the
part of the body which they originate from.
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