Everyone wants to know what motivated Colorado theater shooting suspect James Holmes.

While it is too early to pin down an exact motive, experts think a pattern experts have discovered in past mass shootings may be at play. Something a criminal profiler in Portland calls a resentment hoarder.

Which means all the little things that happen to all of us every day, forensic psychologist Frank Calistro says. That we shrug off every day, these people hold it all in. And build up an incredible amount of anger.

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