this is such a crock....you lose lotza money to the casinos...then why not take it out on the casinos??? it makes zero sense to take potshots at a festival some distance away that has NOTHING TO DO WITH YOUR GAMBLING LOSSES....
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My guess, other than be crazy and probably suicidal, he was ticked off about the noise.
the noise? the windows of the hotel room, im sure were good quality and would minimize the sound of music from what, hundreds of yards away?
The noise??? Be real, this was planned well in advance. He did not just get pissed about concert noise one night and open fire. He chose to massacre concertgoers for some reason(s) as yet undetermined, and he had to spend significant time preparing such an attack.