Dalton, who is expected to be charged Monday, apparently acted alone and there was no continuing threat to the community, Kalamazoo County Prosecutor Jeff Getting said.
Uber's chief security officer, Joe Sullivan, said Dalton had passed a background check to become a driver. The company was "horrified and heartbroken" and had offered to help investigators, he said.
Local NBC affiliate WOOD reported that Dalton may have taken fares in between attacks.
The first shooting occured around 6 p.m. local time at the Meadows Town Homes in the city's northwest, where one woman was shot several times but survived, police said. The next burst of gunfire happened more than three hours later, when police were called to a car dealership, where two men, possibly father and son, were shot dead, authorities said.
The final attack occurred a few minutes later at a nearby Cracker Barrel, where the gunman approached two cars in the parking lot and had a brief conversation with people inside before he "unloaded his weapon into both cars," Kalamazoo County Undersheriff Paul Matyas said. Four adults died there, and the 14-year-old girl was seriously injured, authorities said.
Michigan State Police, according to WOOD, identified the dead Cracker Barrel victims as Mary Lou Nye, 63, of Baroda, Michigan; Mary Jo Nye, 60, of Battle Creek, Michigan; Dorothy Brown, 74, of Battle Creek; and Barbara Hawthorne, 68, of Battle Creek.
The victims "appear to have been chosen at random because they were available," Getting said.
The girl was initially reported dead. But more than an hour later, as doctors were preparing to harvest her organs, she squeezed her mom's hand, Michigan State Police Lt. Dale Hinz told NBC News. She was then able to respond to questions by squeezing her mom's hand several more times, and was rushed into surgery.
"It's an absolute miracle," Hinz said.
Other victims had not yet been identified because their families had not been notified, officials said.
"There's a sense of loss, there's an anger — there's fear — there's all these emotions and then you put on top of that: how do you go and tell the families of these victims that they weren't targeted for any reason other than they were there to be a target?" Getting said.
Dalton was taken into custody around 12:40 a.m. after his Chevrolet HHR was spotted on a surveillance camera leaving a bar parking lot, authorities said. Police found a semi-automatic handgun during the arrest.
"We have 9, 10, 11 shell casings at each of these scenes," Getting said, adding that police were investigating to ensure there no other crime scenes. "These weren't a sudden explosion ...this was done intentionally."
Follow CNBC International on Twitter and Facebook.