Polygraph test are strong instruments for the defense lawyer. However, any criminal defense attorney allowing a client to submit to a poligrafo (polygraph) administered by law enforcement polygrapher is bordering on malpractice. Clients should just submit to polygraph examinations administered by means of an expert hired by the defense team. In this way the consequences (good or poor) as well as the examiner are protected by the attorney/client privilege. What this means is the testing stays a mystery as well as the effects can't be utilized from your client's interests. That said, why should we submit our customer to a polygraph? When they fail the test well, occasionally it is good.
But a lot of times insist upon a plan of action leading to inevitable failure and the recalcitrant customer ignores this reality. Many times, your client insists upon a claim of innocence. Now comes the polygrapher. From the Customer's point of view... a neutral expert. The customer understands the examiner is there to just get facts. The customer doesn't care if he's telling the facts, doesn't negotiate for him, and understands the examiner isn't his promoter. However, the customer also understands there is a good chance he will now be found, if he's been untruthful. The customer understands he'll want to confront reality once found.