A lawyer worth his  salt will not turn his back on the polygraph. A professionally handled polygraph can be the criminal defendant’s best friend.

Despite the critics and naysayers, there is a sizable and growing body of science that supports the validity and veracity of polygraph.

Approximately 15 states admit polygraph results at trial but only if all parties agree to its use prior to the test being taken. One state, New Mexico, allows routine admission of polygraph evidence. On the federal level, the polygraph is allowed only at the court’s discretion, with the exception of the 11th Circuit, which prohibits the polygraph without condition.

The first rule of criminal defense is keeping your client from being charged, which is why a favorable polygraph examination can be a defense lawyer’s best friend. Assuming a client has the good sense to hire a defense lawyer before arrest, a confidential polygraph examination provides a singular opportunity to forestall prosecution. The polygraph is given great deference by prosecutors — a fact little known by the public, but widely recognized among good defense lawyers. This is particularly true in “he said, she said” situations common in sex cases.

Examiner quality is key. The polygraph, like most pattern matching evidence, is not infallible. In the absence of standardized training and licensure, test quality depends on the skill of the examiner. The structure and content of the questions are the most important parts of the examination. It’s up to the examiner to formulate “control” and “relevant” questions, which can be easily answered with a simple “yes” or “no,” as well as logically distinct enough to elicit a physiological response that indicates deception.

Lie detector technology continues to develop in sophistication and accuracy.

Given our government’s institutionalized use of polygraphs, and judicial acceptance of other evidence that is less reliable than the polygraph, the best approach might be to allow this technology into the courtroom on a case-by-case basis, subject to vigorous cross-examination and other tests of reliability. In cases where there are no exculpatory eyewitnesses or alibi evidence, and a polygraph is the only effective means to prove innocence, it should be allowed. Indeed, no one should be denied the constitutional right to present a defense.

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.