Gary Slutkin is an epidemiologist who applies the lessons of disease prevention to the plague of inner-city gun violence. His organization, CeaseFire Chicago, trains former gang members, who know Chicago's gang culture inside and out, as "Violence Interrupters."If gun violence is a contagious disease, these "Interrupters" are the Purell, preventing transmission. They jump in during high-risk conflicts to defuse things and make sure no one gets shot. Brave work. And they're the only ones who can do it; an outsider would have zero credibility and no sense of the context of a conflict.More about the "Interrupters" here. Gary's work was written up in the NYT in May.