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He was known as the Mayor of 95th Street, an angular figure in a cap and blazer who was a fixture of the streets of his Chicago neighborhood. He was an activist who tried to help young people rise above the city's unrelenting gun violence.

But William Cooper, 58, fell victim to the violence he had worked so hard to stop.

On Monday, Chicago emerged from another bloody weekend of gun violence in which 10 people were killed in 35 gunfire incidents from Friday evening through just before midnight on Sunday, the Chicago Police Department said Monday. Among them, the department confirmed, was Cooper, also known as Willie.

Outside the Lilydale Outreach Workers for a Better Community in the city's South Side neighborhood, television stations broadcast an impromptu prayer vigil and a shrine that marked a spot at the nonprofit where Cooper had counseled young people.

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

While the city's gun violence has often left families and neighborhoods reeling, the weekend tally of victims hit particularly hard when it came to light that Cooper, who had made it his life's work to help young people find jobs, was among them.

Cooper was walking near the outreach center at 4:15 p.m. on Saturday when a vehicle pulled alongside him and its occupants opened fire, striking him in the mouth and torso, the police said. According to WLS-TV, an AR-15 assault-style rifle was used in the shooting.

It was not clear whether Cooper had been targeted.

More than 760 people were killed in Chicago last year, according to the police, the most of any U.S. city.

After the shooting, news spread that the city's violence had claimed the life of one of the people working to stop it. "This is a man that was dedicated to helping people in the community," Lamon Reccord, a Chicago activist, said in a Facebook video. "Somebody that was willing to give back to the neighborhood."

"Chicago, let's put these guns down," he said.