Polygraph tests, often called “lie‑detector” tests, are not admissible in court in Pennsylvania. While the science of polygraph testing is solid and reputable, the testing is considered by the courts to be “inherently unreliable” in determining guilt or innocence. Some people can successfully lie without detection, and some people are labeled dishonest when they are giving truthful responses.
Recently, the Pennsylvania Superior Court relaxed the ban on lie‑detector testing in a probation violation hearing. The defendant, a convicted child molester, failed a “therapeutic” lie‑detector test that was a routine part of his sex‑offender therapy. The test was designed to reveal the motives and behavior underlying the defendant’s sexual offenses.
When the prosecution tried to introduce the test result at a probation revocation hearing, the defendant objected. The court disagreed and reviewed the test results. The court held that once the determination of guilt or innocence is complete, lie‑detector testing is sufficiently reliable in later proceedings. The court observed that when a probation program becomes ineffective due to a probationer’s failure to cooperate or achieve rehabilitation goals, the court needs to know and has a responsibility to remove the offender from the probationary program.
The defendant’s failing the lie‑detector test was relevant and competent evidence to justify his expulsion from the program and result in his incarceration. The court cautioned that lie‑detector testing cannot be used in probation programs to investigate whether the defendant has committed other crimes or to reveal any past criminal history. But where lie‑detector testing is part of a structured probation program with clear goals and requirements and where it is focused on the offender’s progress in rehabilitation, the testing results are admissible in revocation proceedings in court.