Unfortunately, perjury is a *very* difficult crime to prove, because you don’t just need to prove that the statement was false, you need to prove that the person “willfully” made a statement which he “does not believe to be true.” Proving that level of state of mind is a very tall order, which is why many prosecutors shy away from bringing perjury charges in all but the most blatant cases (e.g., where a witness subsequently confesses to intentionally committing perjury).
Yep. Just ask Scooter Libby.