I agree that the young man was coerced into his confession. I have significant doubt that he knew anything about the crime in any way. Avery I am unsure about but the nephew was taken advantage of, IMO.
When you watch the interview, the detective kept asking "And then what did you do to her head?" The kid had NO idea. Then the detective says, "I am just gonna go ahead and say it. You shot her in the head, didn't you?"
I was like, SERIOUSLY? And this is standing?!?!?!?!?!
Yeah, that "interview" was brutal. The kid was obviously just trying to guess what they wanted him to say just to get out of there. He had no idea of the implications of what they were getting him to say. When it was over and he asked if he could go back to school now, it was just heartbreaking. He didn't even realize he was going to be arrested.