Let me preface my comments by saying any criminal defense lawyer who allows their client to take a polygraph examination administered by the prosecutor's expert is bordering on malpractice. The only polygraph a client should take is one administered by a polygraph examiner hired by the defense team. This makes the examiner subject to the attorney/client privilege and protects the results (good or bad) with the attorney work-product doctrine. With that said, sometimes it is good when a client takes and fails the test.
Client control and management is often a challenge even among the most experienced defense lawyers. After 18 years of criminal law practice, 14 of which as a defender, some of my clients remain unmanageable, or at least difficult to handle. That's ok, though. Over the years I've learned some tricks of the trade, one of which is the lie detector test.
Many clients refuse to face reality. Reality in the form of hard, indisputable facts, confessions, physical evidence. Prosecutors make offers to settle cases based upon this evidence, but often the client ignores this reality and insists upon a plan of action leading to inevitable failure. Sometimes the client insists upon a claim of innocence despite a mountain of contrary evidence.
In rides the polygraph examiner - from the client's point of view a neutral expert. The client knows the examiner is there only to get the facts. The client knows the examiner is not his advocate, does not negotiate for him, and does not care whether he is telling the truth. But the client also knows if he's lying there's a good chance he'll get caught. And once caught, the client knows he'll need to face reality. Ah . . . much better!
I'm amazed how much more manageable an unruly client becomes after he fails a polygraph. Moreover, the family feels better (assuming we decide to tell them) because their loved-one's claims have been fully investigated and given their proper due. The client is now in a better frame of mind to evaluate offers to settle, trial strategies, etc. I don't imply we roll over for the prosecutor, by any means. But at least the client has a proper grip on their case and can make better, more informed decisions about how to proceed.
So, is your client out of control? Consider giving them a polygraph. If they pass - great - hit the prosecutor over the head with it. If they don't pass, don't worry either. Sometimes the polygraph is for the client's benefit, not the prosecutor's.