The polygraph or the lie detector is one of the most extensively used tools in law enforcement even with its controversial position of providing hard evidence and truly determining a deceptive person from someone who is telling the truth.  While there are some states in the US where polygraph testimonies are admissible in court, others still need a different kind of proof for a person’s guilt in order to be established.  Here are a few resources on the polygraph like what the polygraph is, how it works and so on.

1.    http://en.wikipedia.org/wiki/Polygraph
2.    http://science.howstuffworks.com/question123.htm
3.    http://people.howstuffworks.com/lie-detector.htm
4.    http://www.enotes.com/forensic-science/polygraph-case-histories
5.   http://criminal.findlaw.com/crimes/more-criminal-topics/evidence-witnesses/polygraphs-lie-detectors.html