Florida residents could be forgiven for thinking that polygraph machines were invented quite recently. The devices, which are often called lie detectors, measure stress by noticing changes in an individual’s blood pressure, heart rate, perspiration and breathing patterns. This may sound like modern technology, but the first polygraph was developed almost 100 years ago. Scientists, legal scholars, lawmakers and police officers have been arguing over the reliability of lie-detector tests for almost as long.
Polygraph evidence in criminal trials
Prosecutors, judges and juries tend to like scientific evidence because it is clear cut and not subject to broad interpretation, and polygraph results were once considered to be as reliable as fingerprints. The first people to have polygraph evidence used against them in a criminal trial were two men who were convicted of attempted murder in 1935. The American Polygraph Association claims that lie detectors are 90% accurate, but this view is not shared by professional organizations like the American Psychological Association.
Polygraph admissibility today
The U.S. Supreme Court ruled in 1998 that polygraph evidence was not reliable enough to establish guilt or innocence, but the justices left the question of admissibility up to state lawmakers. In Florida, law enforcement cannot force suspects to take lie-detector tests, but polygraph evidence can be presented in court if both the prosecutor and defendant agree.
Polygraphs and plea bargaining
While an experienced criminal defense attorney would likely advise their client to refuse to take a polygraph test in a police station, they may suggest that they take one far away from the gaze of law enforcement. If the results are not good, the attorney and their client could say no more about the matter. If the outcome is positive, the attorney could use the results to secure more favorable terms during plea negotiations.