I've posted about this before, but at the risk of beating a dead horse: He appears to have had a thing about physically picking people up. He (apparently) did it during the Fairfax attack, he did it to random girls he didn't know in bars, he did it in high school. I find the high school account very telling: That would have been a very big "moment" for JLM, a moment of showing his power that brought positive social attention (if I'm reading the account right). That high school moment could have been emotionally and possibly even sexually arousing. Maybe he kept re-enacting it in some twisted way? That moment of power?
ETA: I don't subscribe to the theory that 2002 rape allegations fueled his rage, and set him off on his course as a sadistic killer. No. You don't become a sadist because of a single incident in early adulthood. He was a sadist long before that. And he reportedly savagely beat at least one of the college rape victims. If the allegation is true, he was already a sadistic rapist by college.
What happened to JM in high school? Where can I read it at?