Let's look at this logically. The most likely killer of a small child is a family member, step parent or neighbor. That is why LE starts an investigation at the inside and works outside.
1. The last thing a DA would want in preparing to go to trial is a year-long set of video clips from LE saying that "Misty holds the key" and "Misty and Tommy admit they were there when Joe killed Haleigh." Thus, if RC was a real suspect in Haleigh's murder, there wouldn't be some switcheroo/ codeword foolishness going on in the media. There would be no talk at all about Joe or Tommy or perhaps even Misty.
2. RC was either at work or not. There will be some kinds of records, witnesses, and perhaps surveillance video at work or on the route to and from work--whether he went the usual way or not. His cell phone will show where he was when he tried to call Misty, how many times he called, and when he called. In addition, there is the AC man who would know whether Ron was there during his visit to the mobile home and whether he talked to him in person or by phone. All of this is pretty much neutral evidence that doesn't depend on Misty, Tommy or any of Ron's relatives.
3. If Ron's alibi didn't hold up, the very fact that he tried to alibi himself would put him at the center of the case, not Misty. He would at that point be (like Scott Peterson, for example) someone who was trying to hide his whereabouts at the time a family member went missing and therefore put himself squarely at the top of the suspect list.
4. If LE had Ron at the center of the case, it would KILL THE CASE IN COURT to have had the wrong people (Tommy, Misty and Joe) publicly held up as the persons of interest, complete with sound bites from LE. The DA would never allow LE to make public statements (in the media or in court) putting the Croslins at the center of the case and saying the Ron was getting a plea bargain. That would be the state manufacturing reasonable doubt.
5. If RC was the one who killed Haleigh, why wouldn't Misty and Tommy just implicate him, tell the story, get the plea deal and be done with it? No matter how much Misty "loves" Ron, her attorney would have told her that he is going to prison for the drugs anyway and she might as well just tell the truth, if that in fact had actually happened, and be the person who got the "witness" deal.
6. Certainly, Tommy has absolutely no incentive--none at all, zero, nada--to do life in prison to protect Ron. Because if Ron, the child's father, had killed her, he would get maximum time. Anyone else might get sentence as accessories or simply be pictured as frightened witnesses, given RC's gun collection and habit of making threats. So the Ron story might have been a "get out of jail free card." But Tommy can't sell that story because it didn't happen. He knows RC was at work and can prove it.
7. I don't know anything about Florida law. So bear with me. If Misty, Tommy and Joe (or any two of these people) were engaged in a conspiracy at the time of the murder or were committing a felony at the time of the murder, in many states all three of them would be convicted of murder. There are many people in prison because one person in a group shot and killed someone while committing a robbery with a gun. That alone would give Misty and Tommy reason to keep quiet about whatever happened with Joe. On the other hand, if RC killed Haleigh in a rage, they would only be witnesses or at best accessories after the fact; if she accidentally took a pill, then the worst case scenario would involved manslaughter, child abuse or neglect, making false reports, abusing a corpse, etc. It wouldn't be MURDER of a child, with likely life in prison.
8. The "enraged that the gun wasn't there" story strikes me as only part of the truth. Then why kill a child? Was the killer high? Was the killer also a pedophile without a record? Did Misty or Tommy catch Joe assaulting Haleigh? I am still not convinced there wasn't a sexual assault.
9. There are, apparently, some forensics available that support the idea that the child was killed in the mobile home and which would explain how and why LE decided a while back that this was not a stranger abduction.
So: RC wasn't involved. Haleigh was murdered in the mobile home by one or more of the three. We still don't know why she died or who all was involved in the murder or where, exactly, they put her.