Another predictive pattern is a significant shift in someone's behavior, Burton says. James Holmes, the alleged Aurora shooter, dropped out of school and died his hair orange. Maj. Nidal Hassan, who is awaiting trial in the shooting at Fort Hood, gave away all his possessions before the attack. Often times these steps indicate someone may soon take drastic action.
"There are patterns, ingredients of a person at risk. If we share those we can mitigate many, many perpetrators," he says. "But there is no software, no expert that can predict workplace violence. Aside from a shift in policy, this imperfect system is the best we can do."
Seth Cline is reporter with U.S. News and World Report. Contact him at firstname.lastname@example.org or follow him on Twitter.