As a part of preparing a strong defense for their clients, many lawyers will enlist the help of a private polygraph examiner to submit their clients to the test. The lawyer may wish to show proof that their client is telling the truth, as well as to confirm or deny results that a law enforcement polygraph examiner previously found. As a result, there is often tension between law enforcement examiners and private examiners. Each side may have trouble trusting the other’s results, but in truth, there are only “good” tests and “bad” tests. As long as the proper procedures are followed, the polygraph test results should be the same, no matter which licensed and experienced professional conducts the test.
Lawyers may also use polygraph test results to verify statements made by witnesses or others who will testify in a case. They can use the results to argue that the testimony should be allowed or that the witness should be impeached for providing false testimony.
Admissibility of Polygraph Test Results
Since there is no ruling from the Supreme Court on the matter yet, the admissibility of the results of these polygraph tests depends on the state. Some states, such as New York, Texas, Illinois, Pennsylvania, and the District of Columbia, find them completely inadmissible. In fact, New York and Texas forbid polygraph use for any employment or law enforcement context. In Massachusetts, polygraph results are not allowed to be entered as evidence; however, they can be used to support probable cause in order to obtain a search warrant.
In most other states, all parties (the defendant and the prosecutor) must agree to admit the polygraph test results as evidence before the exam is given, which is referred to as admission with “the stipulations of both parties.” Only in New Mexico is the evidence admitted the same way as other evidence, with the judge making the final decision.
As a result, they are very rarely used in the trial. However, they still play an important role since the results are often brought in for consideration in other parts of the process: pre-trial negotiations, plea bargaining, witness verification or impeachment, revocation hearings, and sentence recommendations.
As more and more studies come out with support for the modern polygraph test, the rules for admissibility of polygraph examinations are changing across the country. Also, many lawyers are using the exclusion of polygraph evidence at trial as a basis for appeal, and these cases are currently under review by appellate courts.