CHICAGO — A Chicago community activist who worked to fight violence was fatally shot less than a block from the offices of his nonprofit organization, according to police and the man’s relatives.

William Cooper, 58, was shot Saturday afternoon near the offices of Lilydale Outreach Workers for a Better Community on Chicago’s South Side. Cooper was the principal officer of the antiviolence group, which provides jobs to local teenagers.

Police said Cooper was walking when someone shot him from a dark-colored vehicle driving by. Cooper suffered wounds to his torso and mouth. About 20 shell casings were scattered near his body, according to his wife, Sherry Clark, with whom he had three children.

‘‘People are so cold-hearted. How could you take somebody’s life? He helped everybody. I just don’t understand,’’ Cooper’s niece, Patricia Carter, told WLS-TV.

No one was in custody as of Sunday afternoon and investigators have yet to identify any persons of interest, a Chicago police spokesman said.