Do-gooder groups, no less than Hollywood movies, benefit from star quality; and CeaseFire, the group of reformed criminals that intervenes in Chicago street disputes to prevent violence, has Ameena Matthews, a petite charisma machine in a Muslim headscarf. To Steve James' horrifying, inspiring documentary, she lends her magnetic watchability. Her job is to stanch the impulse in some kids to go, as she says, from "zero to rage in 30 seconds." When one young man tells her he fights every day, she smiles and says, "You're too handsome to do that." The daughter of the notorious gang leader Jeff Fort, now serving a 155-year prison sentence on a domestic-terrorism conviction, Matthews channels her father's seductive eloquence into crisis management. The Interrupters, which, like James' Hoop Dreams, was preposterously denied an Oscar nomination for Best Documentary, has a full posse of heroic figures trying to stop crime on the spot. But Matthews is the prime galvanizer. Addressing mourners at the funeral of a teenager who died in gang violence, she says, "We got a responsibility to bring up our community to be vibrant. Whatever it is that's going on, cease the fire, call the truce."