I do not thing Avery or Dassey are guilty of killing TH. Neither of them did it, IMO. I am not saying that Avery is a great guy, or innocent of everything, but I see no way that he killed her, based on the evidence presented.
1. The Trailer - Supposedly she was raped and killed in the trailer. This never happened, it couldn't have happened. They found no TH DNA, or any other kind of evidence of her in the trailer. There is no way that she was raped, attacked or killed in the trailer with no evidence. It is impossible.
2. The Garage/Bullet - Similar to the trailer, if she was killed in the garage, there would be evidence of it. There is none. There is no way to clean up the amount of blood from the floor of that garage, and clean it out of the crack in the concrete. It is impossible.
3. The Bones - It is nearly impossible to cremate a body, to the point of reducing it to pieces of bone in an open fire, in that short amount of time. Burning a body is very difficult, it takes a massive amount of heat, and/or a long amount of time. There is now way that an open fire could cremate a body in one night.
4. The RAV4 - It was found across the street from Tadych's house days after TH went missing. Then mysteriously showed back up at ASY, after it was reported to Deputy Colborne. At the same time, Tadych's buddy texted him (there is evidence of the texts), that it was there, Tadych never said anything about it. Next thing we know, it is found at ASY, with a new battery. It was not stashed at ASY until just before it was found, and there is evidence and witness testimony to prove that.
5. The Blood - First, TH blood is in the back of the RAV, how did it get there if she was killed at Avery's? There would be no reason, or time, to put her in the back if she was cremated that night at Avery's. Her body was placed in the back, and transported in that car, and that is proven by evidence. Second, Avery's blood. It makes no sense for there to be 1 smear of blood. If he was bleeding that much, his blood would be in many places in that car, as would his fingerprints. How do you explain one smear of blood, but now fingerprints or other spots of blood in the car? You cannot explain it.
6. The Cell Phone - There was a voicemail deleted after she went missing. How did this happen? It wasn't Avery, it was her ex-boyfriend. Why was the ex-boyfriend accessing her phone and deleting voicemails?
7. The Planner - She received a call before getting to ASY, and she wrote that appointment in her planner. It is in her planner, and there is testimony of the call. So, it is fact that she had her planner with her the day she went missing. But, we also know that the police were given her planner by her roommate, it was at her house. How did her planner get to her house, if she had it in her car the day she went missing?
8. The Key - Why is the 2nd key, backup key the one that was found? Why would she be using her backup key that day? Sure, there may be good reason for it, but then where are her 1st set of keys? Also, how is it possible that Avery's DNA is the only DNA on that key? Why is TH's not on the key? Why are there no fingerprints on the key? Why is the 2nd key seen in the background during the interview of her roommate, after she was reported missing? The answer is, the key that was found was not the key she was using that day, the key that was found was at her house the whole time, while she used her original keys. They found the RAV4, and didn't have keys, then retrieved the 2nd key from her house, cleaned it well, and planted Avery touch DNA on the key.