Question about the ending (Obvious spoilers)

Well, he didn't murder anyone (except Alex in self defense). He didn't even beat up the guy at work. I guess he robbed two stores for chump change, but if those were his first ever crimes (and I suppose they were) he can probably convince the police that the psycho made him do it. The police are hardly going to arrest a guy for those crimes when he is responsible for solving a murder investigation and bringing the killer to justice. That would reflect badly on the police department, and cause a public outrage.

And it's not a crime to be on a pier at night and have your brother tape a confession from a killer. He can tell the truth. Alex tried to kill him with a booby trapped car. Michael later confronted Alex at the apartment. Tricked Alex into giving chase. No crime there except perhaps for entering the apartment without permission, but who is going to lodge a complaint?

He'll have to explain why he hid Claire's body, that's about it. He'll likely be able to get away with the robberies (which he was basically forced to do, per Alex's commands) because the 2 clerks didn't see his face, and there is no evidence on the tape mentioning this. As long as he doesn't mention it himself. And if it did come up, he'd probably do no more than a couple years for his minor role.
If he wants to keep his good job, he shouldn't mention the robberies.

Yeah, I'm kind of at a loss about the OP's question myself. Unless they are talking about entrapment or something. But neither Michael nor his bro are cops, so the police should be able to use their video as evidence.