Locard’s Exchanged Principle

Locard’s Exchange Principle is a principle used today which was made in 1877-1966 by Edmond Locard. His principle suggests that when contact is made between things such as objects, people and places; trace evidence is exchanged between each thing which can very much result to finding identification of what or who may have made contact on the object. This can most definitely help crime scene investigators use these exchanged trace evidence to find the identity of a criminal in the wrong. Trace evidence can be fingerprints, hair or any other things which contains information about the crime. We can also really get the upper-hand on criminals with the new technology constantly being made especially with the use of D.N.A. This is why this exchange principle has become big in Forensic Science as it can fast track a direct link with evidence to who the criminal is or anyone else present at the crime scene at that time.

Securing And Documenting The Crime Scene

Securing crime scenes is a tedious but important part of the process of collecting evidence from a crime scene. This is of such great importance as the trump card for all crime scene investigators is the use of finding these fingerprints or other things that can clue in on what has happened in the crime scene. Also securing the crime scene is done as fast as possible due to the tampering or contamination of evidence to hide evidence or mislead the scene investigators towards suspecting other innocent people and away from the criminals themselves. In doing so there are certain procedures, steps and guidelines that need to be taken in place to properly secure the crime scene.

The steps to secure a crime scene are:

Provide any emergency care if there are any victims in the crime scene.
Take control of the crime scene by identifying and pointing out the perimeters of the crime scene and where the actual crime took place. Achieve this by putting up physical barriers to let the unauthorized people know where they can and can’t go.
Then look at the area closely with authorized people entering the crime scene as long as they state who they are and why they are here for to prevent non-needed people entering the scene. This can be done by the use of a log book which is used to know who has entered, their position and their reason for being present at the crime scene.
Then start to look at the exits and entry and the whole crime scene for any evidence that could be useful to the investigators.
Make sure the evidence is kept safe from being lost, stolen and being tampered with.

The steps to document the crime scene before evidence is taken are:

(VIDEO) First you must get hands on a camera as compared to drawing or pictures you should take a video to give a layout of the crime scene which cannot easily be seen through still images. The tape should be used with slow camera action for all viewing and must give a brief or general idea of the crime scene.
(PHOTOGRAPHY) Next you would use the camera to get photos for certain and specific detail of the place being photographed. This could also be used to make real life recreations to trace what the criminal would have done. The photo should give reference to the crime scene and the space distributions of evidence with the image of the area surrounding.
(SKETCHES) Finally you would make certain sketches to show the aspect of the three dimensional objects and evidence in the crime scene. You do this as taking photos and videos may distort the crime scene making them have different spot locations in the crime scene. Also sketches help with the scaling of objects as you can physically create the proper size of the evidence for future needs when the documented crime scene information is needed.

Trace Evidence

The types of evidence can be physical, chemical or biological evidences. Trace evidence is defined to be evidence exchanged through two surfaces without notice with the naked eye. It is evidence linked to the Locard Exchange Principle as that basically suggests that every from of contact leaves a trace. Some examples of trace evidence is fingerprints, blood, saliva, hair, footprints, paint, clothes or textile fibers, glass fragments and etc can be found at a crime scene.

Collecting Evidence

When collecting evidence from a crime scene you must take precautions to not contaminate the evidence. To do so you must follow the basic procedures for collecting evidence.

As stated by the US Department Of Justice you must:

Wear gloves and change them regularly.
Use instruments that are disposable before handling any evidence.
Clean your instruments as well.
Avoid coughing and sneezing.
Avoid touching your body when handling evidence.
Put evidence in paper bags or envelopes.
Avoid touching areas where D.N.A might be present.

Chain Of Custody

The chain of custody is a documentation of those in custody of evidence. As always evidence from a crime scene must be used in the court of law to prove the reason on why the suspected party was actually the cause of the crime. To make sure the evidence is valid without the evidence being stolen, destroyed, tampered or contaminated with all those who are in possession of the evidence must put their signature, initials and date on the evidence or evidence packaging. When evidence is found it is given to forensic scientists who analyze the evidence and the forensic scientists go through the same documentation when in possession of the evidence. When the analyzation process is finished the forensic scientists hand it over to police officers for storage who also go through the documentation process. The evidence is only taken out when the evidence is needed for the court of law or when further analyzation of the evidence is needed.


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Title – A Guide for General Crime Scene Investigation: Arriving at the Crime Scene. (2009). Available URL: http://www.nij.gov/topics/law-enforcement/investigations/crime-scene/guides/general-scenes/arrive.htm. Last Accessed Date – 11/08/13

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