It's the disturbing truth that anyone can turn violent or deadly, and it's proven very difficult to identify who's vulnerable and what the trigger might be.

CNN: Autism link to violence is a myth

Asked about the possibility of criminal charges in the Wal-Mart death, Fleming said he would not rule it out but noted that charges would be "very difficult, " as it would be "almost impossible" to identify people in the crowd from the video, and those in the front of the crowd were pushed by those behind them.

CNN: Wal-Mart worker dies in rush; two killed at toy store