A Michigan man who worked as an Uber driver was under arrest on Sunday in the fatal shooting of six people in Kalamazoo, as police investigated reports he may have driven customers of the car-hailing service the night of the rampage.

Prosecutors alleged that Jason Dalton, 45, opened fire, apparently at random, in parking lots outside an apartment building, a car dealership and at a Cracker Barrel restaurant in Kalamazoo, about 150 miles (240 km) west of Detroit.

Two other people were wounded, including a teenage girl who was initially thought to have died.

Authorities could not confirm Dalton was working for Uber during the nearly five-hour shooting spree on Saturday evening. He was arrested without incident on Sunday while driving away from the parking lot of an area bar.

An Uber representative confirmed that Dalton was a company driver and had passed background checks. The representative referred questions about whether Dalton was working at the time of the shootings to police.

The victims ‘appear to be chosen at random, because they were available,’ Kalamazoo County Prosecuting Attorney Jeff Getting said. ‘They were shot multiple times, multiple - nine, 10, 11 shell casings at each of these scenes.’

The carnage in Kalamazoo, a city of about 75,000 people, was the latest in a series of mass shootings that have elevated gun control as a campaign issue in the November U.S. presidential election.

The attack also prompted renewed interest in how Uber vets drivers, who use their personal vehicles to ferry customers at prices that are generally below those of established taxi companies. Critics say the company’s vetting process is flawed because it never meets with potential drivers in person.

Uber says on its website that it has an ‘extensive’ driver screening process that includes collecting detailed information from potential drivers and using the investigation service Checkr to vet them. Other websites and databases such at the Dru Sjodin National Sex Offender Public Website are used as well.

WOOD-TV, a Grand Rapids station, quoted police as saying they were investigating reports Dalton dropped off Uber fares at a hotel and then killed four women and wounded a 14-year-old girl at the nearby Cracker Barrel. The teenager was in critical condition, Michigan State Police said.

In an emailed statement, Uber’s chief security officer, Joe Sullivan, said the company was in contact with police to help with the investigation.

An Uber passenger, Matt Mellen, told CBS TV affiliate WWMT that he had tried to alert the company after a wild ride with Dalton about an hour before the first shooting was reported.

He said Dalton introduced himself using a different name from the one listed as a driver. He then sped through medians and across a lawn, and Mellen jumped out at a stop at about 4:30pm.