Some mass killers have struggled with severe mental illness and the experts say there is a link between serious, untreated mental illness and violence.
FOX News Radio's Jessica Rosenthal talked with some people who have struggled with their mental health to find out more about what goes on inside the minds of people capable of violence:
The man who shot people at Congresswoman Gabrielle Giffords' event in Tucson, was later diagnosed as schizophrenic. The UC Santa Barbara killer, admitted he was depressed. Some like the UCSB killer who've written manifestos or made videos, indicate severe anger and a desire for revenge.
Elliot Rodger from YouTube video: "If I can't have you. Girls, I will destroy you."
Mental health experts say many mass shooters increasingly isolate themselves before the violent act.
Richardson: "I'm going to get to them before they get to me, Cause I know, someone's going to do wrong to me. That's the way I was thinking."
Jim Richardson who was once diagnosed as bipolar and schizophrenic, says it was easy to think about violence and even be violent toward others--
Richardson: "Quite a few people."
Richardson: "Physically. I had no remorse, no conscience, nothing at that time."
He tried to commit suicide. Former Green Beret, Troy Wynn thought about it too. He says when he hears about mass shootings--
Wynn: "It's such a familiar thing with me. Like I've been to these dark places. And, by the time I got to where I was and started feeling some of those feelings of suicide or even homicide, I felt like I had no other options."
Jessica Rosenthal, FOX News Radio.
Follow Jessica Rosenthal on Twitter: @JessicaFOXNews