Un diagnosed mental illness.

That's what one TV commentator said about the Vegas shooter.  And, it's kinda true by default.  We believe anyone who would shoot 500-600 innocent strangers to be mentally ill.  A week of investigation has failed to find (or at least report on TV) any sort of motive, history, or association that would give a motive, or suggest some kind of mental illness.  So, we figure he must have been acting out a horrible mental illness when he opened fire, and no investigator has found any evidence of mental illness before the shooting.  On the other hand, they have reported that he had been buying a lot of guns, legally, for a year before, which surely suggests that what ever it was, it started back when he started buying all the guns. 
   And this is really unusual.  In all the previous awful cases, the shooter had given clear signs of mental illness or some kind of dreadful political fanaticism.  Unfortunately these signs were ignored until it was too late.  In this case alone, we haven't seen any signs of mental illness or political craziness after a week of investigation.