SteveK, et all... regarding the unrequited love scenario, wouldn't there be a sexual assault involved with that? I do not remember if LE has said there was no sexual assault or if we all assume there was none. Because there was so little time and LE did say the perp killed and left.
IMO no.
To be clear, I don't think there was evidence of a SA here. But that omission doesn't make me rethink anything, because I don't think "love" and SA are inevitably intertwined. There are murders all the time, arising from "love" gone wrong, in which no SA occurred. And there is lots of SA in which there is really no deep feeling other than a desire for sex or power at any cost.
Here, I'm theorizing that this was a male who for some reason wasn't up to par (or at least perceived that way by self and/or others). Short. Younger. Awkward. Unathletic. Ugly. Perhaps any or all of those. And who wanted MB's favor and admiration (maybe because she was the teacher), didn't get it, and then decided that if he couldn't have her, no one could.