I agree with most who think that Shawn is probably the one who disposed of the body. I think he is capable of killing Hailey either by accident or for the purpose of keeping her from telling something on him. I think that Billy was way too trusting of Shawn and she absolutely should have not had a man with his (ahem), "hobbies and interests " living in her home with her kids.
Billy seems to really be waiting on pins and needles to find out if this body is Hailey. I have no official source for that but I do have reasons, so MOO. Because she hopped in the car and came straight home as soon as this body was discovered, I believe that she truly does want to know what happened to Hailey and has no reason to "run". If I'm wrong, then boo on me; I believe that she believes whatever lies Shawn tells her.
Did Shawn have help from someone to hide Hailey's body? His family has never been helpful in the investigation since Hailey disappeared. They seem like the type who would cover for Shawn no matter what - even for murder. If Shawn hid something on the family property for a day or two until he could get rid of it, I don't think they would tell.
If Shawn had not quit his job that day, if he hadn't been acting weird when David came home, if he hadn't lied about where he was, I would have to consider others who could have killed Hailey. But he did quit, and lie, and act guilty. He did sell drugs and have child *advertiser censored*. He did get a thrill from acting like a killer and watching himself on video.
I Hailey hadn't been found in his old stomping grounds, a place very familiar to him, close to his mom's home where he felt safe, I'd wonder if it could be someone else.
The pings, the lies, the fantasies about murder and sex, and the body all lead straight back to Shawn. Billy needs to throw him to the wolves and save herself. MOO
I know that most people are convinced that Billy is just as evil as Shawn, and I can see why they think that. I just have a different take on it, and that's okay.
