The police wiretap caught Josh, Michael, Alina and Steve discussing various issues. Josh (I believe it was) offered his sister hydrocodone in a syringe for a headache. It has been floated that Josh may have sedated Susan via food on the night of her disappearance. Liquefied hydrocodone seems like an easy way to do that. Smothering her with a pillow while she was unconscious might be the way he ended her life. If he broke her nose while he was doing that, it could account for the small coughed-up blood drops on the floor and also the blood swipe on the back of the love seat. Maybe she woke up and struggled some.
He apparently melted something metal in his garage around that time, though. Like his many many many trips to the dumpsters around town, it's hard to account for everything....
The wiretap summaries show Josh and the Powell clan directing their anger at Chuck Cox, Jennifer Graves, and the Mormon church. If someone had run away and made me a world-famous murder suspect, I know who I'd be mad at. They do say derogatory things about Susan, but nothing about finding her alive to get out from under suspicion. She didn't take her wallet so presumably she had no ID--or money. Josh had her cell phone (with its sim card removed) in the minivan. (No innocent explanation for that, btw.) How far could she have gotten?