I have always felt that this murder was motivated by uncontrollable desires/emotions of the perp. I think the scenario described by you milopedes is probably what happened. The only part that really throws me is this - if it was sexual why stab her?
I can see this attack being done out of anger - anger towards women - or anger towards authority - the university or something of that nature. Almost an "I'll show them mentality".
I think often times, for the type of guy I see think committied this crime, the sex and violence are intertwined. It could have been anger toward women as well.
Either way, you raise a lot of good points. Of course, we are simply left to speculate unless new facts come to light.
I haven't had time to research any of this, but there are several factors I'd like some "professional" (i.e., retired detective, profiler, etc.) to give me some details about . . .
1. Psychology of the "one-stab", if such information is out there. More than likely, there is something out there on "stab versus shoot".
2. It has been awhile, but I'd like to read up more on the "blitz" attack. Besty was suddenly, and violently, attacked with this knife. I know some, but have not read much in awhile as I am slowly getting back into this as a hobby (sick, huh?) if you will.
I'm more prone to believe that a rageful attacker would do more than simply stab once, despite the sheer amount of force I think was required, and then leave the scene. Hence, I think it was more sexual in nature.
Pure conjecture here, but maybe he was sexually frustrated or was reminded some person from his past that had some "sexual meaning" to him?