I've put off posting here for ages, because I just don't think I can go through all of the info/links/posts, etc. that contribute to the theory I've decided on after so many years of following this case. I will say this, however: If one looks at everything available online regarding the ll, goes through the map/travel info, and considers the contacts in the last hours from the ll, it seems pretty obvious what happened.
SK was behind in rent and a bit down about that, as evidenced by several things that have been said by family. An example is his defensiveness toward his father in their last conversation. I think it's plain that he was feeling financial pressure. LL says that they "made arrangements", or something to that effect, about SK resolving his late-rent issue.
LL is involved in a "business" related to procuring old/unused prescriptions and reselling them. (Some of these people died soon after this was investigated.) (Due to the financial need; rent "arrangement"; travel, etc., I have concluded that SK worked for him ) There are folks who posit that he, himself, used the drugs, but I've seen nothing that would vaguely suggest this. SK was a clean-cut, "all American", mission-completing, church-going Mormon. I think it would be quite easy for him rationalize that the ll "prescription business" was legit, or at least "quasi-legit" at least in a way that selling cocaine, etc. isn't. Heck, I can see how it could be rationalized as helping people: It can be very difficult to get prescription narcotics for chronic pain, and I have much sympathy for those who suffer such and can't legitimately obtain effective pain control. So, maybe he realized that, although there was something slightly shady about the business technically, he was able to rationalize it, or maybe he thought it was totally legitimate. (I doubt it, because I do see some efforts to conceal this activity.) Either way, he's working for the ll and his people, making deliveries. Hence, "working out an arrangement" for the late rent.
So, what was the trip about to see the woman he barely knew? (Not his "ex-girlfriend", at least by my memory.) Who knows, but my best guess is that he was traveling in that direction on his deliveries and remembered where she lived. I think he and others did a work project at her home some time back. He wasn't married and likely wanted to see her again, thinking that the work he did there before was enough of an introduction. He says he's on his way to Sacramento because he doesn't want anyone to know about the crazy work he's doing. Legitimate business or not, most mission-completing, college graduate Mormons his age aren't running all over Utah making deliveries. Not prestigious, certainly.
So, along comes an appointment to deliver/procure for delivery some of these prescriptions, and one of the people he's dealing with decides he knows too much/wants the drugs then and now for himself/who knows, and that's the end of SK. If the phone didn't ping right there in SSA, my guess is he got in someone's car outside of the view of the security video. At any rate, the reason the ll kept calling him is he needed to get a hold of him and didn't realize, at least immediately, what had happened. My guess, though, is that he figured it out PDQ.
Look up the ll, folks: There is your answer.