Lie detectors, also known as polygraphs, are a popular tool among U.S. law enforcement agencies for detecting deceit. The first lie-detector instrument was created in 1895, and the polygraph was developed in 1926. The Supreme Court has deferred judgment to the courts of each jurisdiction to determine whether polygraph exam results are admissible in court.
A polygraph is an instrument that collects physiological data, such as respiratory activity, sweat gland activity and cardiovascular activity, from a person while he is being questioned. Polygraphs are based on the idea that a person who is lying will experience physiological changes in blood pressure, pulse, respiration, body temperature or skin conductivity.
Lie-detector tests were used by police as early as the late 1800s. In 1895, Cesare Lombroso developed an instrument that measured changes in blood pressure. Notable advances were made in 1914 by Vittorio Benussi, who created a device that measured respiratory changes, and in 1915 by William Marston, who developed the systolic blood-pressure test that is used in modern day polygraphs. In 1921, Dr. John A. Larson developed a device that recorded both blood pressure and galvanic skin responses. Larson's device was further developed by Leonarde Keeler, who ultimately produced the polygraph in 1926.
Polygraphs are popular among federal, state and local law enforcement. The legal community also frequently makes use of polygraphs in both criminal and civil cases. The Employee Polygraph Protection Act of 1988 generally prevents employers from requiring applicants or employees to undergo polygraph examinations.
The U.S. Code and the Federal Rules of Evidence are both silent on the admissibility of polygraph examination results. The U.S. Supreme Court has deferred judgment to the courts of each jurisdiction to determine whether polygraph exam results are admissible. As a result, polygraph exam results are excluded in some federal circuits and states but are admissible in others if the parties previously agreed to admissibility before the exam was given.
Arizona, California, Florida and Nevada permit the use of lie-detector results in court if all parties agree beforehand that they will be admissible. On the other hand, Illinois, New York, Pennsylvania, Texas and the District of Columbia completely exclude polygraph exam results even if all parties want to admit the results.
In Massachusetts, polygraph exam results may not be entered into evidence but they can be used by police to obtain a search warrant. Florida requires sex offenders to undergo polygraph examinations, but the test results are strictly for rehabilitation and treatment purposes and cannot be admitted in court as evidence against the offender.
Law enforcement cannot compel someone to submit to a polygraph examination.
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