How did they keep the perv from getting Elliot arrested? Since they didn't kill him, all he had to do was walk into a hospital or call a news channel. I would think new ADA would've been happy to arrest a "bad cop".
The other three detectives (Fin, Olivia and Munch) all covered for Elliot.
They could all say whatever they wanted. If he went to a hospital and they called the news media, all those bruises (and Elliot's bruised hands) would've proved they were all liars. They must've had something on him.
Otherwise, the show just crossed a line that shouldn't have been crossed and implied that they were going to kill the guy if he talked.