CHICAGO -- A community activist who worked to fight violence in Chicago was fatally shot less than a block from the offices of his nonprofit, according to police and the victim's relatives.

William "Willie" 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 anti-violence 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.

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His wife told the Chicago Tribune that her late husband "did a lot for the community."

William "Willie" Cooper CBS Chicago

"He is just the rock of the family -- it just destroyed our family," Miltonya Covington, the victim's niece, told CBS Chicago. "Not just a loss for family, but also for the community."

Debbie McBounds lined up with others at a makeshift memorial Sunday evening. "It's heartbreaking. We love him. We will miss him," McBounds told CBS Chicago.

She added, "He would always try to help anyone -- the kids who needed to go to college, he gave money for that, anybody who needed help with their rent."

Bamani Obadele, a friend and fellow activist, told the station, "It is our responsibility to not allow Willie Cooper's murder to be in vein."

No one was in custody as of Sunday afternoon and investigators have yet to identify any persons of interest, Chicago police spokesperson Anthony Guglielmi told The Associated Press. He said detectives are trying to determine whether Cooper was targeted or the victim of a random shooting.

"It's too early to say at this point," Guglielmi said, noting that investigators were trying to track down any surveillance video that may have captured the shooting.

Relatives arriving at scene of the shooting were in tears. They gathered with other family members in front of the nearby offices where Cooper had worked.

There have been 372 homicides in the city of Chicago this year, according to the Chicago Tribune.