The bloke must have had a serious psycho problem. Fortunately it didn’t manifest itself while he was flying with passengers.

They say he killed his ex-girlfriend.
I’m no shrink, but I’d guess that there are a lot of people out there who are capable of killing a loved one but who would never think if killing strangers.

In other words, they may be jealous, violent, controlling nuts…but not a complete sociopath.