Also, speaking of leaping to conclusions, why do you assume there was "no follow-up" on the Vegas shooter? Do you suppose the authorities, from local on up to federal, just didn't feel like it? Decided to wash the squad cars that day instead? Too busy chowing down on donuts? In your imagination, did they just shrug helplessly and say, "Ah, why bother?"

To the best of my knowledge, they were never able to determine a motive for the shooting, despite extensive investigation. Either the information required has not (and may never) come to light or its significance has not been recognized, or there was simply no motive beyond a desire to kill people. Sometimes we don't get all the answers to our questions.

Evidently they discovered child pornography on his computers, and also on his brother's computers. Perhaps he had reason to believe he was under investigation and that the hammer would drop at any time, and decided to take as many people down with him as he possibly could.