bbm
Elle, I have the impression that Tommy first took the polygraph, then was told he failed, and then gave up the truth to his lawyer and the person who administered the polygraph. I think he hated jail and thought he could do better than his sister at fooling the LDT, and got desperate enough to attempt taking it.
I agree with your reasoning and think that both Joe and Tommy came back to the MH, possibly with the idea of all doing drugs. Joe may have also wanted to try and get his hands on Ron's gun. I think LE has known certain parts of what happened that night, but not the whole story. It appears that Tommy, and possibly Misty, has finally cracked and provided the details.
One thing I am fairly certain about is that whatever happened that night in the MH is something that neither Tommy nor Misty wanted their families to find out about because, had they learned the truth, their families would have left them. This is why they kept their secrets, because they would have lost what they cared about most. And now they will.
It's pretty clear that Ron had no involvement. I'm sure that he suspected various people, including Misty, but had no more luck than LE getting to the truth. He tried in his own way to find out what happened. He must have had an incredible love for Haleigh to have married someone that he had suspicions about, thinking he could get her trust so she would break down and tell the truth. He sure underestimated her.
I think the reason that LE said that both parents were not considered suspects, but did not clear them, was that they actually had a smaller group of suspects than the public realized. If they had officially cleared both Ron and Crystal, then it would have been a tip off to Misty, Tommy, and Joe that LE was narrowing down the candidates. LE didn't want them to be on their guard, hoping that they would slip up.