Experts Find No Definitive Profile Of A Killer

President Obama heads to Arizona today to give a speech honoring the victims of this weekend's shooting rampage in Tucson that left six people dead and 14 people injured, including Congresswoman Gabrielle Giffords. 22-year-old Jared Loughner is charged in the shootings, and police now say he got off 31 shots from a high-capacity magazine, before bystanders were able to stop him.

Some House Democrats now want to limit the sale of that type of ammunition. But meanwhile, with so many warning signs, why didn't someone investigate Loughner more deeply. And if they had, would they have been able to stop the tragedy? Investigative Journalist Bill Dedman of msnbc.com examined a 1999 Secret Service study of assassins and tells us there is no profile, and in fact, most had no mental health treatment or made previous threats.