If he didn't, then money or a jealous woman would/could be the motive. We heard from that character, Carroll (or his attorney, Muna), that there was a kidnap plan, and that they were planning to extort money from the Rochas. It has occured to me that maybe SP told the gang that say $250k would be no problem for the Rochas. Suppose for a minute that (IF SP didn't do it), after Laci disappeared, SP got the feeling that the Rochas were kind of po'd at him, and he'd better not ask them! Then, say, he was trying to come up with the money himself to get her back, like selling Laci's car, trying to sell the house, but he knew dang well he'd better not tell anyone of his sleazy plan. Suppose Dirty and Skeeter gave him two weeks or so to come up with money, and SP couldn't or wouldn't. He would have been afraid of Dirty and Skeeter and wouldn't want to toss their names out there, and he certainly didn't want to go to jail himself, so .....
As for the jealous lover, maybe we should look more carefully at his neighbor who seemed to be around at all times. Just a couple of ideas--if Scott didn't do it himself.