I don't see why nobody's even considering that she may have committed suicide.
People do it every day.
So she takes photos of the van Steven is selling, drives some distance away from it but still around the county and offs herself? Then the cops find it, shoot her a couple times with a 22, throw some blood around the RAV4 and plant the evidence on the Avery property? That scenario is equally as out there as anything outside of someone on the Avery property being the murderer.
The more realistic than anything else scenario goes like this:
1. TH shows up to SA's property, something happens and is killed, lets just assume by SA for now.
2. SA puts her body in the back of the RAV4, BD comes over and sees it
3. SA plans to dump the body in a pond (as said in BD's confession), but decides instead to burn the corpse at the quarry
4. Body burns too slow, SA collects what he can and takes her to his house where he can burn tires along with the body
5. SA stores core on lot, planning to crush it later
6. Cops fine car, plant a ton of evidence on top of their already strong suspicion that SA is the killer
That scenario has less holes, matches up with what we know about the crime scene, and is way less complicated than anything else anyone has suggested. It also jives with some details that came out of BD's confession that weren't forced out of him.
The thing I want to stress again though, is that I definitely think he was fucked by the system and should not have been found guilty based on the evidence presented. Just that the honest, most simple explanation for what happened is that someone on that property killed her.