Locard’s Exchange Principle | Forensic Handbook. 2013. Locard’s Exchange Principle | Forensic Handbook. [ONLINE] Available at: [Accessed 11 August 2013].

Protecting the Crime Scene. 2013. Protecting the Crime Scene. [ONLINE] Available at: [Accessed 11 August 2013].

FBI — Trace Evidence. 2013. FBI — Trace Evidence. [ONLINE] Available at: [Accessed 11 August 2013].

Evidence Collection Guidelines. 2013. Evidence Collection Guidelines. [ONLINE] Available at: [Accessed 11 August 2013].

FSC Forest Stewardship Council Australia (FSC-AU) · Chain of Custody. 2013. FSC Forest Stewardship Council Australia (FSC-AU) · Chain of Custody. [ONLINE] Available at: [Accessed 11 August 2013].


Crime Scene Investigation


In order to find the criminal from a crime scene forensic scientists need to inspect the scene to find evidence, they are highly trained and will do anything to help the victim restore what they have lost and bring justice to the criminal in court.

As you all have probably watched CSI, scientists look hard to find evidence, and also to secure it properly they have to do a lot of careful stuff. They will always find one piece of evidence no matter how bad or good the criminal is. A criminal can leave many types of evidence, including DNA, fingerprints, footprints, hair, skin cells, blood, bodily fluids, pieces of clothing, fibers and more. At the same time, they will also take something away from the scene with them.

Locard’s Exchange Principle

Forensic scientists use Locard’s Exchange principle to find, document, and collect evidence from the scene of a crime, and anything or anyone that may have come in contact with the crime scene. As Locard’s exchange clearly states, Toute action de l’homme, et a fortiori, l’action violente qu’est un crime, ne peut pas se dérouler sans laisser quelque marque” or “Any action of an individual, and obviously the violent action constituting a crime, cannot occur without leaving a trace”. This means that forensic scientists will always find evidence to support the victim.

Securing The Crime Scene

This is the most important aspect of the investigation, any evidence that has been tampered with, can alter the results of the investigation. Any mistakes made by poorly trained policemen and forensic scientist can lead to a failed investigation.

The Police Departments and Forensic scientist trainers have too include lessons on how to secure the crime scene.

The first officer on the scene of a crime should approach the scene slowly and carefully, the officer may be responsible for arresting to criminal and/or saving the victim. The first officer should take mental or written notes about the condition of the scene as it was when the officer’s first arrive and after the scene has been stabilized. He should also note down when he entered and left the crime scene etc. The officer MUST not tamper with the evidence involved. Also the area of the crime scene should be restricted to authorized people only. The investigators should be protected as well, leaving an investigator alone could be dangerous.


Police need to document evidence found at the crime scene. Collecting all evidence isn’t always necessary, investigators only have to find just enough evidence to win the cattle in court. Failing to document the evidence properly can lead to the evidence not being useful on court. In order to document the evidence and crime scene properly investigators have to photographs of the evidence before it is collected. After it is found investigators need to record the information about the evidence on the Evidence Custody Sheet. Taking 200-400 photos of a crime scene when your an investigator isn’t un-ordinary especially if the crime scene is big.

The investigators must take photos from all perspectives of the crime scene eg. take photos that show an overall view, a medium view, and close-ups. Contaminated evidence may also be collected but it is most likely not used for court.

Trace Evidence

The Investigators have a whole unit just for trace evidence they are called the Trace Evidence Unit (TEU). They have to identify and compare trace materials. Trace evidence is evidence that can be traced back to the suspect and identify them. It can also show us what and how something died. The collection of evidence may include:

Hair- this can tell us whether the object is animal or human, this can tell us race, naturally shed or forcibly removed this evidence may also be examined by the Mitochondrial DNA Unit.

Fiber- this can tell us if the object is natural or man made, torn material can be traced back to where it came from.

Feathers- this can tell us what bird the feather belonged to. This evidence can determine if the bird took something from the crime scene.

To make sure the evidence isn’t contaminated forensic scientists have to:

– Use clean equipment, the equipment must be cleaned before processing evidence.

– Contact must be restricted if needed touch the evidence only with gloves.

– Adequate lighting, easily cleaned surfaces, and a physical environment designed to restrict excessive air currents, static electricity, and general foot traffic. is needed in the area of the crime scene is also needed to prevent contamination.

– Any contact, condition, or situation that could cause contamination or otherwise compromise the trace evidence examination must be documented

– Collect and store evidence in separate packages to prevent contamination.

– Document any problems or accidents.

Chain Of Custody 

Chain of custody or (CoC) is basically when the evidence is chronologically documented showing the forensic scientists seize, control, transfer, analyse, and the final position the physical or electronic evidence. This is used to help the judge know that the evidence hasn’t been tampered with and is in the same condition as it was back at the crime scene.

This is important for criminal cases and for the drug testing of athletes, traceability of food products and proof that wood is cut from sustainably managed forests.

This is used when collecting and securing evidence so that all of it can be used in the court. Any tampering or contamination of evidence can lead to non-use of the evidence or loss of battle in the court.