Daughter of Black P. Stones and El Rukns leader Jeff Fort, Ameena Matthews was a drug ring enforcer in her youth. But after having children of her own and converting to Islam, Matthews committed herself to combating the same impulses of crime and violence that plagued her own upbringing.

She became an “Interrupter,” one of a group of former gang members who intervene to prevent inner city bloodshed as part of the nonprofit CeaseFire. CeaseFire is the brainchild of epidemiologist Gary Slutkin, who applied the lessons of his decade working for AIDS and cholera prevention in Africa to addressing urban violence as an epidemic.

Director Steve James (Hoop Dreams) and author Alex Kotlowitz (There Are No Children Here) tail Matthews and her colleagues as they step into emerging conflicts and offer counseling to the most troubled families, in their Kartemquin Films documentary The Interrupters. It premieres in the Sundance Film Festival Friday 1/21. All four screenings there are sold out.