What makes some people commit mass shootings?
While details about James Holmes, the suspect in the Colorado movie theater shooting, are still emerging, he joins a group of men accused and/or charged in the deaths of 76 people over the last 13 years.
From Columbine to Virgina Tech, Fort Hood to Tucson, the rampages were unexpected and impersonal. Houston psychologist Dr. Laurence Abrams said behind them all are accused shooters who had an overriding emotion.
"The anger is usually there in some form or fashion," said Abrams.
That anger usually causes family and friends to distance themselves from the person.
"People will tend to back off when you're angry," Abrams explained. "Parents will back off. They don't want to make the kid mad, especially a big kid, like a 22-year-old or 24-year-old."
That can lead to isolation, which is another common trait he said is in most mass shooters.
"You're going to find alienation. You're going to find disconnection from people around. You're going to find some bitterness about some event."
Just what made Holmes, 24, angry is not yet clear, but Abrams said it is not usually a sudden event but rather a growing, gnawing, nagging feeling that gives the suspect time to plan and plot until he finally pulls the trigger.
"Obviously, it's been in the works in his mind for awhile," said Abrams. "And why that day or why that event or why any given day, you don't know."