False confessions are a leading cause of wrongful convictions. According to the Innocence Project, about 25 percent of the documented DNA exoneration cases involved incriminating statements, full confessions or guilty pleas by innocent suspects.
The polygraph is an important tool in the extraction of false confessions. Despite the well-documented inaccuracy of the polygraph, police in North America (less so in Europe and other areas) still rely heavily on the “lie detector” and its even less accurate cousin, the voice stress analyzer, in the investigative process. If an innocent suspect fails the polygraph exam, police will use the results to persuade him or her that they must be guilty. In some cases, police will tell the suspect that they failed the exam even when they didn’t in an attempt to obtain a confession.
Given the polygraph’s inaccuracy and record of being used to obtain confessions, I am continually amazed to come across cases in which defense attorneys encouraged their clients to submit to a stipulated exam whose results can be used in court, where polygraph results are generally inadmissible.
Polygraph examiners are almost always current or retired law-enforcement officers who are likely to see guilt where a more objective person might not. If the suspect “fails,” the exam, the polygraphist can testify not only that the suspect showed signs of deception but also that he or she supposedly made incriminating statements, exhibited body language suggestive of guilt or used deep-breathing techniques or other measures to outfox the polygraph. As a result, stipulated polygraph exams are usually the kiss of death for an innocent suspect, and many plead guilty rather than face having the polygraph results used against them at trial.
The polygraph industry in the United States, in particular, has done an outstanding job of perpetrating the myth that the polygraph exam is a benign scientific pursuit of the truth. Many people who take a polygraph exam, even if they pass it, conclude otherwise. Karen S. Beers, a respected legal investigator in Colorado, writes about how intimidating a polygraph exam can be and more about the problem of false confessions here. The New York Times has an excellent story about why people confess to crimes they didn’t commit here.