Once back in Chicago, however, friends kept telling him about the epidemic of violence in inner-city neighborhoods. As he began to study the problem he came to the view that gun violence in poor neighborhoods did indeed resemble the epidemics he had treated in Africa. Maps that charted gun violence showed clustering — just like maps tracking infectious diseases. The greatest predictor of violence was a prior violent incident, which also mirrors epidemics.
In 2000, he founded CeaseFire (now known as Cure Violence), a Chicago-based organization that treated violence in one such local cluster — in West Garfield, one of the toughest neighborhoods in the city — as a public health problem rather than a criminal justice issue. Shootings dropped dramatically.