When I first started "lurking" on Websleuths, this heartbreaking case was one of the first that caught my eye, and literally made me cry. First off, I know this has nothing to do with a theory, per say, but I noticed on the 1st Police Report (linked under the "Facts" thread) that Haleigh's sex was listed as "Male". That must have been a typo on the part of the transcriptionist, right? I also noticed Haleigh has Turner's Syndrome, a chromosomal abnormality that can result in heart and thyroid, among other health, problems.
Anyway, on with my theory. Like many of you, I, unfortunately, believe the sweet little girl is deceased. I am also (almost) positive that there was no "mysterious intruder" that came in and took her during the night. I believe that either a) there was an accident sometime within the night, perhaps caused by neglect (Misty was out partying) - perhaps Haleigh fell and hit her head, or something along those lines, and when Misty arrived home she panicked, knew there would be multiple party witnesses available to testify she was not home watching the kids, and thus that she would most likely be charged with neglect of some kind, perhaps even resulting in the death of a juvenile, and for that reason created the intruder story. My second theory (b) is that Misty WAS at home at the time of little Haleigh's demise. Perhaps Haleigh wouldn't go to sleep, or she wet the bed, or perhaps Misty had a "house guest" (hmmm) and Haleigh witnessed something Misty was afraid she'd reveal to Ron later, and for any of these reasons Misty "lost it" on Haleigh and the little girl died as a result of child abuse. Whether this was chronic, ongoing child abuse, and this particular night Misty just went too far, I really don't know. Has there been any documentation of longer term child abuse with these kids? Anyway, so those are my theories. Since Ron was at work, I don't think he had anything to do with it, although I think he now probably knows what happened, and/or that Misty may have even told him what happened even before the initial 911 call (hence Ron calling Misty a b$&*#, etc, during the call.) Why Ron hasn't come out with the truth yet is up for speculation. Perhaps because he initially lied, he is afraid to now tell the truth, knowing he'll be charged with aiding and abetting. Maybe he doesn't want to lose his other two children, and keep what remains of his family unit intact. Who knows, really?
And finally, as far as where sweet little Haleigh's body is, your guess is as good as mine. I do have some ideas as to what could have been done with her by Misty and perhaps one of Misty's closest friends or other boyfriends, but they are too terrible to even think about, much less write here. Unfortunately, I don't think her body will ever be found, and unless someone with inside information breaks down and confesses, a certain person/people will get away with this crime.