OK I just finished it. I missed it when it first aired but I have to say, what an amazing show, just as good as sone of the great TAL episodes.
So, my boring opinion is the same as everyone: The case was far from being sufficient to sentence anyone to life in prison. The investigation was not finished.
I can only come up with 3 main possible theories:
1) Adnan did it and Jay helped him. This is the 'easy' solution, the one that makes the most sense. The biggest changing factor is Jay's involvement, he has a very bad memory and either he can't help but make up details (even when doesn't really remember) or he's trying to minimize his involvement and creates a mess of a timeline in the process.
Pros: There is nothing too far fetched about this theory.
Cons: There is no proof, and some inconsistencies. And sure, even if it makes some kind of sense, innoncent until proven guilty.
2) Jay was involved in about the same way but he's covering but somebody else, framing Adnan. Somebody he's afraid of.
Pros: That would explain some things. Like why is he still afraid for himself and his family TODAY. Why was he so afraid of that 'west side hitman' then.
Cons: This is very far fetched, what are the odds? But then: he was a drug dealer in Baltimore, so he had to know some fucked up people. Also that theory makes Adnan really unlucky. But then again: A lot of murder cases end up being about very very bad luck (some have linked to examples here). Also, yeah is Adnan unlucky because he gave his car to the one that end up being involved on killing his ex-girlfriend, or is it this fact that created a interraction between Jay and Hae that day and/or made Adnan the guy that was so easy to frame?
3) Some Random guy (serial killer or whatever) did it. Jay is pathological liar and a teenager always trying to impress everybody/ always needs to have a story to tell. He had the car of the ex-boyfriend the day a popular girl dispeared. Make up this rumour 'this girl is dead, I know who did it, I saw her in somebody's trunk'. He starts living the lie, like 'i need to get rid of my clothes' in front of his girlfriend (why would he do that with her if hes trying to protect her?). Well, when the body is found, he realizes he's fucked. Given the rumours he has been spreading, the police will get to him, and on top that he's a drug dealer. So, through hours of untaped interrogations he changes his story until he come up with one that satifies the cops. Don't forget he a scared kid in way over his head, the detectives can make him say whatever they want.
Pros: it explains why his own girlfriend of long time NEVER believed him, because the guy was always full of shit. And we can all agree now that the guy is a liar anyway. So why not?
Cons: Again, what are the fucking odds? And also: THE CAR. the fact that he appears to know where it is. But then again: maybe he has heard about it/found it himself/the cops told him of the record and wanted him to point to it because it helped with their case. But yeah I know, this is extremely far fetched.
I realize I didn't think too much about Jay being the killer himself. I don't know why, but of course it is a strong possibility. Probably number 2 after Adnan (for motive reasons).
Sorry for the long post. And for my bad English.