What are the procedures used to collect and preserve evidence?

Regardless of the type of evidence that is to be collected from a crime scene, the evidence needs to be ‘bagged and tagged’. This meaning that the piece of evidence needs to be stored in an appropriate bag that will preserve the evidence and contain a description of what the piece of evidence is presumed to be. For example if a blood stained sweater was found at a crime scene, the most appropriate container to place it in would be a paper bag, this is to ensure that the item is clearly secured reducing the possibility of interference. In addition, a paper bag would be chosen in comparison to a plastic bag, as the bag may steam up thus disregarding any bodily fluids which may be present, which will potentially hinder the investigation. All evidence that is collected at a crime scene should be tagged, with consistency. The information that must be detailed on the piece of evidence includes the police case number, the date, location of collection, the collectors name, a description of the item and any a serial number.

Essentially the chain of custody establishes who has had contact with the piece of evidence, the days and times the evidence was handled, the circumstances for the evidence being handled and what changes were made in the evidence if any.

For example if a sample of blood was to be collected from the crime scene, the SOCO would use a cotton swab to swab the substance off the surface, if the presumed blood is dry they’d placed several drops of distilled water onto the swab to moisten the substance to enable it to be collected. The swab would be then placed into a small transparent cylinder that would be air tight, to prevent the evidence being contaminated. Whilst the evidence is being collected the SOCO must ensure they are wearing adequate PPE at all times, to prevent the contamination of the evidence.

Within the investigation of Paul Morin hair fibres were collected from the vacuum bag of Paul Morin's car. This was completed by using a specialist hoover that is used solely for criminal investigations. As once Paul Morin's car was obtained from his pathway it was held within the facility of forensic centre in Canada. It was there that the inside of his car was vacuumed in order to obtain any potential evidence which will aid the investigation. The vacuum bag was then emptied within the centre under strict conditions, which includes the forensic scientist wearing personal protection equipment. An electronic microscope was used to analyse the hair fibres obtained from the car, in order to identify if the fibres matched the fibres found on Christine Jessop's body.
The evidence is preserved by ensuring that it was contained within an evidence bag that is sealed at all times unless it was under analysis. The evidence bag used should have been of plastic, this it to ensured that it is secured and prevents the possibility of contamination. 

Furthermore, the physical evidence obtained from the criminal investigation was a witness statement. The witness statement was collected by asking potential witnesses who lived in the surrounding area of Paul Morin's house to provide information regarding the case. The individual is required to write about their personal facts and opinion regarding the incident, the investigator must ensure that it is then signed by the witness. This is to declare that the individual only told the truth within the statement. 

The witness statement is preserved through the process of chain of custody, as it ensures that it is noted of any personnel who comes into contact with the statement in order to distinguish who had access to the evidence. Furthermore, the evidence is preserved through the use of the signature of the witness, which declares that they wrote the statement.