a mistake in judgment, certainly, or are you saying that they intentionally shot knowing that they would get ten years in prison for it? LEO’s often kill unarmed men in a lapse of judgment and don't even get a reprimand.
In my opinion, Compean either panicked or "went Rambo." Neither alternative displays much judgment.
That being said, Compean argued he saw a weapon, but that argument was rejected by the jury.