CHICAGO (CBS) — Investigators trying to determine why a 45-year-old man shot eight people in southwestern Michigan on Saturday were looking into reports the suspect picked up passengers as an Uber driver in between shootings.

Jason Brian Dalton was expected to face multiple charges of murder in connection to a shooting rampage that left six people dead and two wounded Saturday night in Kalamazoo County. Among the victims were a retired teacher and a 17-year-old high school student. Dalton was expected to be arraigned on Monday.

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Police have said Dalton has no criminal record, and targeted his victims at random.

The shooting spree began around 6 p.m. Saturday, when Dalton allegedly shot a woman multiple times in the parking lot of a Kalamazoo apartment complex. Police and witnesses said she saved the lives of several children, including 12-year-old Joi Coleman, when she put herself between the kids and the suspect.

“He shot her once, and she was still running and then he shot her again, and she fell, and she asked, ‘Joi help me,’” Joi Coleman said.

That victim is expected to survive.

Joi’s mother said Dalton came back four times after shooting her neighbor, as the children were running for safety.

“He backed up and attempted again as they were running into the house, and then missed,” Meghan Coleman said.

More than four hours after the first shooting, Dalton allegedly gunned down a father and son at a car dealership about eight miles away. Killed were Richard Eugene Smith, 53, and Tyler Daniel Smith, 17, of Kalamazoo.

About 20 minutes after that, police said Dalton opened fire in the parking lot of a Cracker Barrel Restaurant, shooting five people in two cars. Four of those victims died, including 60-year-old Mary Jo Nye, 62-year-old Mary Lou Nye, 74-year-old Dorothy Brown, and 68-year-old Barbara Hawthorne. A 14-year-old girl who was shot was in critical condition on Sunday.

Surveillance footage from the Seelye Ford Kia dealership and Cracker Barrel helped Kalamazoo authorities quickly identify the suspect.

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Dalton was arrested without incident about two hours after the last shooting, when police spotted his vehicle leaving a bar parking lot. A semi-automatic handgun was found in his car.

Mark Dunton and his friends heard about the killing spree Saturday night, and got nervous when Dalton picked them up in a car that matched the one police had been looking for.

“My buddy Scott actually said something to him; said, ‘Hey, this isn’t the HHR, you’re not the guy, are you?’ and he kind of just said no,” Dunton said.

Dunton and his friends might have been Dalton’s last customers Saturday night.

“It’s crazy to think that someone could have gone out and just done all these horrible things, and just came with a straight face like he’s just going to work doing his job,” Dunton said.

Dalton, a married father of two, had no prior criminal history. His neighbors were in shock.

“We’re wondering what might have caused him to do this; and, of course, we’re thinking about all those innocent victims, and the families. It’s just horrific,” Gary Pardo said.

Uber confirmed Dalton was a driver for the ride-sharing company, and had passed a background check, but would not confirm if he was working Saturday night.

“We are horrified and heartbroken at the senseless violence in Kalamazoo, Michigan,” Uber Chief Security Officer Joe Sullivan said in a statement. “Our hearts and prayers are with the families of the victims of this devastating crime and those recovering from injuries. We have reached out to the police to help with their investigation in any way that we can.”

Investigators have said they are looking into whether Dalton picked up passengers before, in between, or after the shootings.

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Police have not yet determined a motive for the shooting, as he had no apparent connection to any of the victims.