"This is a simple, senseless double homicide committed by a bunch of cowardly thugs," Police Superintendent Terry Hillard said. "These are murderers. They killed two innocent people."
One person was being held for questioning, but police said they had made no arrests.
Autopsies showed that Anthony Stuckey, 49, and Jack Moore, 62, died from multiple injuries and blunt trauma, Cook County medical officials said. Both deaths were ruled homicides.
The accident happened Tuesday evening in the middle-income Oakland neighborhood on Chicago's South Side after the victims' rental van veered over a curb and crashed into a stoop filled with people, injuring three women, one critically.
Detective Phil Cline said the men were using the van to move furniture and it wasn't known what caused the van to swerve.
The mob beat the two men to death with their hands, feet, bricks and stones, reports Chelsea Irving with CBS Affiliate WBBM.
"So many people were beating these men. I can't even tell you, it was so many," onlooker Marya Williams told CBS.
The group beat the two men with their hands, feet, bricks and stones, police said. The size of the group wasn't immediately known.
Both men lived in the area.
"They hit them with bricks that came off the side of the building," Taquita Mixon told the Chicago Tribune. "They didn't have a chance. It was a brutal beat-down."
Julia Mitchell, 29, who lives across the street from the accident scene, said she arrived and made eye contact with one of the two men, lying on the ground.
"His eyes were big and he was scared. He looked at me, blinked once and exhaled, and I knew that he had died," she said.
Virginia Stuckey said her son was helping Moore move some items from an apartment and would not have been driving because he did not have a driver's license. She said her son was an unemployed day laborer and factory worker who had lived with her since January.
"I really can't believe that anyone would kill someone like that," said Stuckey, 72. "I hope they send them to prison."
Toni Preckwinkle, a city alderman who represents the area, said the predominantly black neighborhood has been improving over the past several years.
"It has struggled for decades with demolition and abandonment, gang and drug activity," Preckwinkle said. "In the last five or six years, there's been a lot of change, new construction and renovation."
A 26-year-old woman who was struck by the van was in critical condition Wednesday. The others — 17-year-old and 18-year-old women — were in fair condition.
Cornell Ousley grew up in public housing across the street from the accident scene.
"It shouldn't have happened, but I understand how these individuals got hurt. Two wrongs don't make it right. You do something to one person down here, you did it to the whole community," he said.
But the Rev. Bamani Obadele, who lives nearby, said people in the community don't support street vigilantism.
"It was dead wrong," he said.