AC1.3 - Explain how evidence is processed
Types of evidence
Physical evidence
Any tangible evidence from a crime scene could be considered physical evidence, for
example: fingerprints, bullets, blood samples, fibre evidence. It is an important aspect of
criminal investigations and so great care must be taken to avoid contamination to ensure it is
admissible in court.
Testimonial Evidence
This is evidence which is in the form of a written or spoken statement. This can support
either the prosecution or the defence. The written statements have to be disclosed to either
side in order so they can prepare for court.It must be admissible, meaning it must comply
with the rules of evidence. Police will take statements at the crime scene, and the media
can be used in order to help witnesses come forward. Evidence is given in the witness box
and the opposing side has a chance to question it. Defendants themselves cannot be forced
to give evidence and vulnerable witnesses may give evidence by video link.
Locard’s Exchange Principle
- Edmond Locard - a key figure of forensic science
- ‘Every contact leaves a trace’
- Materials from the crime scene will be present on the offender
Other categories of evidence
- Non physical - non-tangible evidence - eyewitness, opinions from an expert witness
- Real evidence - any evidence generated by criminal - blood splatter, shell casing
from bullets
- Demonstrative evidence - representation of an object designed for a courtroom -
photos, diagrams, x-rays and models
- Known evidence - source can be determined with certainty at the scene without the
need for laboratory testing - blood samples taken at the scene
- Unknown evidence - do not know the source until testing is done in a laboratory later
- blood splatters
- Individual - evidence that can be linked to only one source - DNA samples,
fingerprints, wear patterns
- Class evidence - common to a group of people or objects which can’t be linked to
one source - hair without root, material fibres, blood type evidence
Collecting, Transferring and Storing Physical Evidence
, Blood
- Blood at the scene would initially be collected by crime scene investigators and then
analysed in a forensic lab by forensic scientists and specialists
- The blood should first be allowed to air dry, and if any fabric has blood one it then it
cannot be folded as this would mean that the blood would transfer.
- Once the blood has been collected it is packaged and then sent to the laboratory for
analysis by forensic scientists as soon as possible.
- Luminol is used to detect blood as it reacts with haemoglobin in the blood and when
in complete darkness, it will show as a blue light if blood is present
- Even if the blood had soaked through carpet, blood could still be traced
- You need to be careful to not contaminate stains with each other
- Blood that is in liquid form should be picked up with a gauze or cotton pad and then
allowed to dry thoroughly
DNA Evidence
- Avoid touching the tips of the gloves as this could cause contamination
- The case no. , your name and item no. should be on the swab box before the swab is
taken
- Blood has to be refrigerated in order for it to be conserved correctly
- Samples are compared to the suspects sample in order to see if it is a match
- Evidence should be air dried before packaging
Semen
- Often found on clothing or bedding
- It needs to be air dried before it is sent off for analysis. Once it is dry, it should be
placed in a paper bag, sealed inside a polythene bag, and then sealed again and
labelled
- A polythene bag is used to ensure no contamination takes place, and so it is also
important that everything is bagged separately
Hair and Fibres
- Protective clothing is worn so the scene is not contaminated
- Fibres are picked up using tape at the scene and are then wrapped in paper, sealed
and sent to the laboratory
- The fibres are looked at under a microscope, where things such as a person's race
or where the hair came from can be identified
- The analysis can be used to identify the colour of clothes the suspect was wearing
- Drug use can be detected through analysis of the hair follicles.
- Shannon Matthews case - hair analysis showed she was drugged before she was
initially kidnapped
Fingerprints
