We are frequently asked whether it is advisable to take a polygraph examination. This is a question where you really need to consult with an attorney over the phone. Usually, the disadvantages to taking a polygraph outweigh the advantages.
There are really only two major reasons the government would want you to take a polygraph:
1) They are trying to get you to make a statement; or,
2) They are legitimately on the fence about whether to bring forward charges and are offering you an exculpatory polygraph.
In our experience, exculpatory polygraphs are typically only used in drug cases. In other words, some commands will use an exculpatory polygraph to assist in determining whether you knowingly used drugs.
The value of taking a polygraph is usually minimal. If you pass the polygraph and they go to trial anyways, the results of the polygraph are inadmissible, but the government can still use your statements against you. In other words, you can't tell the jury you passed the polygraph, but they can tell the jury what you said.
Our general philosophy is to hire our own confidential defense polygraph expert to conduct the polygraph. If you pass the polygraph, we use it. If you fail, no one will ever know.
At the end of the day, whether to take a polygraph requires case-specific advice. A free consultation is definitely advisable.