“My goal is to save a life.”

Last night “violence interrupter” Ameena Matthews was on The Colbert Report to talk about The Interrupters, which airs on FRONTLINE Feb. 14.

Shot over the course of a year in Chicago, the film follows Ameena and two other interrupters, Eddie Bocanegra and Cobe Williams, as they attempt to intervene before situations turn violent: two brothers threatening to shoot each other; an angry teenage girl just home from prison; a young man heading down a warpath of revenge.

People listen to her, she tells Stephen Colbert, “because I’m considered a credible messenger. “I’ve been there and I’ve done that. I’ve been out there in the streets of Chicago.”

Watch the segment, embedded below, to learn more about where she believes violence comes from and why she treats violence as a disease.