So years ago, I took my wife on a "secret" honeymoon. I didn't tell her, or anyone else where we were going. This was "B.C." - before cellphones, so I left contact info in sealed letters with her family.
Now I know why they opened the letter before we drove a block a away.
I don't believe the police/sheriff's dept have released any info on motive, so far. A friend of mine is involved in the investigation, and they have several things that they believe played a part, but nothing that would be a clear motive last time I talked to him (Friday).
ETA: ... unless he just wasn't telling me something. I suppose that's possible.