Way back when the Simpson murder occurred, a friend of mine said, "It was OK for OJ to pass Nicole around to his black football friends, like Marcus Allen, but let her show some interest in a Jewish accountant, and OJ goes blind with jealous rage."
I thought it was funny at the time, possibly true, but this crime reminds me of that.
It makes some sense, in the viewpoint of a narcissistic psychopath. If HE decided to pass HER around, then he was exercising ownership, and his status among his peers increased. If SHE exercised independence, then that was an intolerable wound to his ego.