There's no evidence that it's a myth. It's a common theory (among most liberals I know) that torture doesn't work, but given its long history — and the comments of pratical practitioners of torture; e.g., a French Algerian War agent — I have to wonder if torture doesn't indeed work when applied judiciously.

This is not to say that (a) the US uses or approves of torture or (b) that torture is morally correct. I merely note that if disapproval is based on the it-does-not-work theory, then if I can prove it does work, where does the arguement go?