Thomas said that she last heard from Lori the Saturday before she disappeared, when she received an e-mail with her new address in North Carolina. I'm sure there is an apartment with that address. MH wouldn't have to make up a phony one. You're pretty good at putting pieces together, so how about this? He was supposed to leave first, with Lori following at a later date. We know he wasn't enrolled, so we can assume that his trip back there was for backround information. He scouted likely places that rented reasonably priced apartments, and gave the info to Lori.
I'm contradicting my last theory, but after reading everyone else's replies, I'm going to guess that he was planning on killing her before the supposed move. The pregnancy was just a fluke. Her questions just moved the timetable up a few days. Her disappearance would of course prevent him from moving or starting school. This would also explain why he was able to hide the body so well. He planned it carefully.
Of course he wasn't completely clever, because phone calls are logged and so are credit card purchases. Right down to the last second.
Is this plausible?
I agree that this is a possibility... Your might be right... it could be that he could have snuck back and killed her (while in NC) and try to pull off "I was in NC, I couldn't have killed her."
Maybe this idiot thought he could get away with even by doing it on Sunday night. Something is not right unless Lori was very good at putting up a front in front of others. She was happy and still talking about moving to NC on Sunday night. The people at the party said everything seemed fine. Also no one has said they heard a fight between them at apartment complex (well no one has said anything in the media).
I don't know if he was really out to kill her... Maybe he thought he could get her out in NC and keep up the lies or convince her the move was a good thing after they got out there despite all his lies if she found out about them later. Something tells me he was trying to get away from SLC, his family and hers. Maybe they ended up arguing Sunday night and maybe she threatened to leave him. and he killed her out of fear she would leave him and expose him to his family.
I also don't think the pregnancy is what set him over the edge at this point. It was his lies and getting found out about or the possibility of loosing Lori over his lies made him snap. (If I can't have her no one can... mentality)