The grey talon assassins are a very special group for one reason. They have never been caught. They are impossibly hard to find; many doubt their very existence. Once one has found them, they can be sure the job will be done… for the right price of course.
It is not considered a crime if a ship's crew mutinies against a captain that is obviously unfit for the post (dangerously incompetent, insane, or overly cruel). Assuming, of course, that they can prove it.