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The Polygraph

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Andrea Poon

on 27 October 2012

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Transcript of The Polygraph

The Polygraph By Andrea Poon History of the Polygraph When polygraphs are used How it works Performance of a polygraph by a forensic examiner Real life cases Role of polygraph Major signs The polygraph was invented by Sir James Mackenzie in 1902. But his lie detector was less successful and not as advanced.
So in 1921, John Larson invented the modern polygraph machine; and it is used now a days in police interrogations and investigations. In a criminal investigation, the polygraphs are used in some cases related to civil lawsuits or criminal trials.
Polygraph testing is sometimes used as a support for evidence, or a way to determine if a witness is trust able. The polygraph works by using the machine to record several different body responses as the individual is questioned. In a criminal investigation, polygraphs are used when hard evidence is not available or not enough.
Evidence taken from the polygraph testing itself does not automatically mean the suspect is guilty. But the polygraph is rather seen as a valuable tool that when is combined with other types of evidence, it will help lead investigators to a successful resolution of the crime. A Forensics examiner would hook the suspect to the machine and start to ask tester questions that would have a truthful answer to them ie. their name, date of birth, where they live etc. Then they will start asking questions about the issue/situation, and then can compare the reactions from the test questions to the investigation questions to see if the person was lying or not.
These experts are trained so that they can tell the difference of when someone is being truthful, or when they are lying. A real life case that investigators used a polygraph was: The Jorelys Rivera Murder Case.
7-year-old Jorelys Rivera went missing
Her body was found three days later in a dumpster
special agent gave the suspect a polygraph test.
read story here:
http://jimfishertruecrime.blogspot.ca/2012/03/jorelys-rivera-murder-case-polygraph-as.html My References This is a Polygraph... The polygraph can sometimes play a pretty important role in criminal investigations... Examiners can compare the body response to specific questions and then they can verify if the subject is being truthful or not from what a they are saying. http://jimfishertruecrime.blogspot.ca/2012/03/jorelys-rivera-murder-case-polygraph-as.html http://www.pinow.com/articles/311/when-should-a-polygraph-be-used http://home.total.net/~galcar/html/brief_history_of_the_polygraph.html Some of the major physiological signs of stress triggered by the sympathetic nervous system that the polygraph test analyzes are: blood pressure
respiratory rate
electro-dermal activity
heart rate
body language http://herbertmetzgar.com/faqs.html#Q4 The End Accuracy of polygraph Polygraph testing results are still considered as an unreliable source due to the many people's variables as to why the readings can come back as the person lying. Using a polygraph test as evidence in court has a slim chance of proving the suspect as guilty or innocent. This type of test only is being considered when both sides agrees for the polygraph test to be admitted. So this type of test is not used very often. Useful or not... sometimes they are useful, but most of the time they are not.
should usually prefer hard evidence or more visual evidences to be shown in court instead of a polygraph test. Youtube video: How Polygraph Works
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