My 5p take on the "survey" was that it read as oddly amateurish and poorly-constructed for generating useful qualitative content. I'm a bit surprised that something like it would be approved for post-graduate release and am not sure how it would have passed required ethics boards or been deployed within subject populations (source: I research, teach and supervise at an R15 uni).
BK is likely IMO to a planning thrill-killer a la Stephen McDaniel, someone who sees himself though a Nietzschean and/or fanfiction lens, and for whom the act of murder is a heroic act of self-knowing, and the ultimate subversion of stuffy social mores blah blah blah.
It's all boll*cks of course, and he will also be the guy who gets het up about someone queue-jumping at an ice-cream stand, but my guess is that when the truth of his "** why ** emerges, it will be sad, stupid and self-glorifying, and won't enlarge human knowledge one whit.
And it was the white Elantra, after all. Fine work by LE and I look forward to the day when we can all forget BK and remember the dead.