Locard's Exchange Principle
Locard's Exchange Principle states when a crime is committed wherever that person steps, touches and leaves even unconsciously would serve as evidence against him. Anything can be left at a crime scene from DNA, fingerprints, footprints, hair, skin cells, blood, bodily fluids, pieces of clothing and fibers.
For example in 1912, a Frenchwoman by the name Marie Latelle was found dead in her parents house, her boyfriend at the time was named Emile Gourbin he was questioned by police but told them he was playing cards with a couple friends at the time of the murder. But when Locard looked at the corpse of Latelle and thought underwise to scrap underneath Gourbins nails to gather skin cell samples, sure enough Locard found samples of a pink make up, while at that time make up was well known it wasn't mass produced so Locard did some research and found a chemist that custom made the make up for Latelle.
This is an example used in Forensic science due to the fact forensic science is researching the body or corpse of the victim, so what Locard did in this case was he recognized that Marie Latelle was strangled to death so he suspected her boyfriend and underneath his fingernails he found traces of Latelle's make up and her skin cells. This serves as a example that with human contact a trace of evidence is left on both of them.
For example in 1912, a Frenchwoman by the name Marie Latelle was found dead in her parents house, her boyfriend at the time was named Emile Gourbin he was questioned by police but told them he was playing cards with a couple friends at the time of the murder. But when Locard looked at the corpse of Latelle and thought underwise to scrap underneath Gourbins nails to gather skin cell samples, sure enough Locard found samples of a pink make up, while at that time make up was well known it wasn't mass produced so Locard did some research and found a chemist that custom made the make up for Latelle.
This is an example used in Forensic science due to the fact forensic science is researching the body or corpse of the victim, so what Locard did in this case was he recognized that Marie Latelle was strangled to death so he suspected her boyfriend and underneath his fingernails he found traces of Latelle's make up and her skin cells. This serves as a example that with human contact a trace of evidence is left on both of them.
Securing The crime scene
When securing a crime scene the first officer present at the scene is responsible for confronting any suspicious personal and preventing any disturbance to the evidence presented, But sometimes this is not possible because the first officer is detaining a suspect. But once other officers arrive at the scene the police start taping around the area of the evidence. For example if the scene of the crime is a 7-11 store the police will tape the front door and other things such as windows, then they would tape the back door or any other way of getting inside of the scene. Once this is done the police allow only authorized people to access the scene such as investigators or forensic scientist to analyse the information at the scene of the crime.
Trace Evidence
Trace evidence is the residue that is left between the interaction of 2 surfaces or substances without being noticed. For example when a man barefooted walking on tiles he would leave his skin cells and footprints on the floor.
Examples of Trace evidence are blood, dna, hair cells, skin cells, fingerprints and footprints.
Examples of Trace evidence are blood, dna, hair cells, skin cells, fingerprints and footprints.
procedures used to collect evidence
- Plastic Bag: All evidence that is dry but also in large quantities should be stored in plastic bags.
- Plastic Containers: All evidence that is moist is collected and contained in leak proof containers, but under no circumstances should moist evidence be left in a container for more than 2 hours for fear of micro organisms growing which will lead to the destruction of moist evidence
- Magnetic Powder: Magnetic powder is used in the process of collecting fingerprints and then photographed to be scanned in the national database
- Paper Packet: a paper packet is used to collect small amounts of dry evidence instead of putting it in a plastic bag to prevent contamination, Examples of evidence that is put into plastic packets are hair fibers
- Plastic Containers: All evidence that is moist is collected and contained in leak proof containers, but under no circumstances should moist evidence be left in a container for more than 2 hours for fear of micro organisms growing which will lead to the destruction of moist evidence
- Magnetic Powder: Magnetic powder is used in the process of collecting fingerprints and then photographed to be scanned in the national database
- Paper Packet: a paper packet is used to collect small amounts of dry evidence instead of putting it in a plastic bag to prevent contamination, Examples of evidence that is put into plastic packets are hair fibers
chain of custody
The Chain of Custody is the process of which evidence is stored and is allowed to be presented in the court of law, In which in forensic science it is used to identify, record and track all evidence from the scene of crime.
bibliography
Crime-scene-investigator.net. 1981. Protecting the Crime Scene. [online] Available at: http://www.crime-scene-investigator.net/evidenc1.html [Accessed: 6 Aug 2013].
Locard's Exchange Principle. 2012. Locard’s Exchange Principle | Forensic Handbook. [online] Available at: http://www.forensichandbook.com/locards-exchange-principle/ [Accessed: 6 Aug 2013].
Science How Stuff Works. 1912. HowStuffWorks "Locard's Exchange Principle". [online] Available at: http://science.howstuffworks.com/locards-exchange-principle2.htm [Accessed: 6 Aug 2013].
Wiki.Answers Locard's Principle. 1913. What is one example of how the Locard Exchange Principle is used in a crime scene?. [online] Available at: http://wiki.answers.com/Q/What_is_one_example_of_how_the_Locard_Exchange_Principle_is_used_in_a_crime_scene [Accessed: 6 Aug 2013].
Definitions.uslegal.com. 2001. Chain of Custody Law & Legal Definition. [online] Available at: http://definitions.uslegal.com/c/chain-of-custody/ [Accessed: 9 Aug 2013].
Locard's Exchange Principle. 2012. Locard’s Exchange Principle | Forensic Handbook. [online] Available at: http://www.forensichandbook.com/locards-exchange-principle/ [Accessed: 6 Aug 2013].
Science How Stuff Works. 1912. HowStuffWorks "Locard's Exchange Principle". [online] Available at: http://science.howstuffworks.com/locards-exchange-principle2.htm [Accessed: 6 Aug 2013].
Wiki.Answers Locard's Principle. 1913. What is one example of how the Locard Exchange Principle is used in a crime scene?. [online] Available at: http://wiki.answers.com/Q/What_is_one_example_of_how_the_Locard_Exchange_Principle_is_used_in_a_crime_scene [Accessed: 6 Aug 2013].
Definitions.uslegal.com. 2001. Chain of Custody Law & Legal Definition. [online] Available at: http://definitions.uslegal.com/c/chain-of-custody/ [Accessed: 9 Aug 2013].