He didn't do his job. And it was demonstrated in court.
As for Compean, maybe he and Aldrete-Davila could've gotten cells across the hall from each other so both of them could look at each other and think, "I am such an idiot."
BULL! What did Ramos do? The only testimony as to what Ramos did was Ramos own testimony. He did not see any "tampering" with the scene. He did not explicitly report shots to the supervisor as has been mentioned. He only knew that someone had fired shots(he was in a ditch when he heard shots) and that he fired once at a fleeing suspect. So your "special" view of the testimoy, is truly "special".