It is implied throughout this episode that Luke had done something wrong, including the offer of immunity.
Luke believed his mother was being raped by an intruder. No such immunity would be needed, as deadly force would be justified in this situation, even in New York.
There is nothing that Luke did that required immunity. See more
I don't think that Luke intentionally shot Trey. He truly believes that his mother was being assaulted.
Dominick Carisi Jr.
I agree. Counselor, look. Luke had no clue that his mother was using his friends sexually. He just happened to walk in. I mean, if he hadn't gotten into an argument with his father that night, he never would've been there in the first place. Nicole is the one who's lying, not Luke.
[looking at her phone
And this proves it. Lab results are back. Traces of fresh semen were found on a towel in ...