I just finished reading a good book that was published in the late 1990's, "A Beautiful Mind." As you might recall, this was the story of John Nash, the genius mathematician who was also suffered from paranoid schizophrenia (the movie version of the book starred Russell Crowe). Dr. Nash miraculously was able to recover from this debilitating condition, and committed no violent acts while he was struggling with the malady. Young Jared Loughner of Tuscon AZ was unable to control his diseased brain, and he committed mass murder and grieviously wounded Rep. Gabrielle Giffords.
Nineteen people were shot; six died. The confluence of random events that brought these people together are boggling to consider. One generally doesn't worry about being murdered when heading out to an outdoor event hosted by one's local congressperson. It is a very rare occurence.