Sometimes a polygraph (“lie detector”) examination report is helpful in the defense of a criminal case. Such reports are not generally admissible at trial, so that the jury will probably never see the report. But it might be a useful tool in convincing either the prosecutor or the grand jury not to proceed with the case.
Sometimes I see criminal-defense lawyers offering to let prosecutors’ polygraph examiners (usually police officers) question their clients. This is generally sloppy lawyering, if not downright ineffective assistance of counsel. I even took over one case in which the previous lawyer had not only let the polygraph examiner from the Sheriff’s Office examine the client, but then also let the investigating officer and the polygraph examiner interrogate the client in the lawyer’s absence!
Government polygraph examiners use the polygraph as a tool to get confessions. Being told that the machine says you’re lying provides tremendous motivation to change — or at least explain — your story. Sometimes a police polygraph examiner will tell the accused that he has failed the polygraph regardless of the real result.
Any accused who is going to take a polygraph exam should, if only for that reason, first take one from an independent examiner. The exam costs (in Houston) less than $1,000. If the accused fails, the result never goes any farther than the lawyer, who knows that (for whatever reason) the client can’t pass a polygraph exam and shouldn’t waste his time taking the government’s exam.
If the accused passes, however, he may have a result that the prosecutor will accept. If the prosecutor still insists on a police examiner performing the examination, the client knows going in what to expect and knows that he can pass a polygraph examination. He will not be susceptible to the police polygrapher’s interrogation tactics.
(As in any context, any accused who is going to be talking to the government should be thoroughly rehearsed in not allowing the discussion to go any farther than it has to.)