Common rumor says yes. Scientific backers say its still reliable. But either way, the polygraph will do no good (at best) for the innocent.
The problem is one of universal perception. By themselves, polygraph tests cannot acheive reasonable doubt. But they are still accepted as a way of bolstering evidence for a trial. Yet the very existence of the question "Can you cheat the polygraph test?" drives a dagger into the heart of an innocent defendant's case.
For a moment, place yourself on the jury for a murder trial. Let's say that, according to the prosecution, the defendant has voluntarily taken polygraph tests and failed each one. Even though it was voluntary, every result showed that he or she lied about being innocent! Wouldn't this be, to the heart and to the mind, a powerful evidence of guilt?
Now turn the situation around, and note that the defendant passed each polygraph test, implying that they told the truth. It's not hard to imagine this creeping doubt, an underlying awareness that the defendant could have cheated the polygraph. Even if you accept the 'passed polygraph' as a sign of innocence, where is the sense of conviction you would feel if they had in fact failed it?
We can more readily accept it as proof of guilt, but absurdly, we cannot accept it as easily as proof of innocence.
Of course, no one would cheat a polygraph to prove themselves a liar. But the test is at odds with the rights of the defendant to be presumed innocent until proven guilty. The door only swings open in one direction.
That is one reason most states no longer accept the lie detector test. However, it may still be admitted if both parties - defense AND prosecution - consent. This is certainly true in Nevada, and let it be noted that a prosecutor doesn't need to give a reason for blocking it. But if the polygraph says a person is innocent, what are the chances the prosecutor is actually going to allow it in as evidence?
Let's say you were on trial for murder. You are innocent, but your freedom (and perhaps your life) is on the line. Yet, you have passed several polygraph tests, and each determined that you were truthful about your claims to innocence.
Congratulations. It doesn't mean a thing.
Polygraphs didn't help Kirstin Lobato, either...despite the fact that she passed three of them. Remind me where the justice is again?