As authorities look for the reasons why a Michigan man allegedly embarked on a mass shooting spree over the weekend, the ride-hailing service Uber is addressing his record as a driver with the company.

Critics say the episode could bring more attention to concerns about the fast-growing service, which has been dogged by controversy on the road to becoming one of the most valuable privately funded companies in the world.

Jason Dalton, the man arrested in connection with the Kalamazoo rampage that left six people dead, is a former insurance adjuster who had been working as a driver for Uber's ride-hailing service. Authorities were investigating unconfirmed reports he may have picked up passengers in the hours before and after the rampage on Saturday.

San Francisco-based Uber has been one of the most successful tech industry startups in recent years, as millions of customers have flocked to use its smartphone app for hailing rides in 380 cities around the globe. The company says its drivers are independent contractors who use the app to help find customers and schedule trips.

Private backers have poured more than $10 billion into the company, under terms that value the business at more than $50 billion — making it the biggest in a recent wave of tech firms that have grown to enormous size without taking the traditional step of selling stock to the public.

But since its launch in 2009, Uber has faced criticism for a pricing formula that can send rates skyrocketing at times of high demand, and for side-stepping regulators and licensing requirements in some cities where it's opened for business. And after several reported assaults by drivers, critics have also complained the company should do more to screen drivers and guard passengers' safety.

Some of that criticism has been raised by competitors and regulators who argue that Uber's success has come as the company has expanded while seeking to avoid the strict licensing and permit requirements that traditional tax companies face.

"I do think this is an outrageous incident that's going to draw more attention to this issue," said Dave Sutton, spokesman for "Who's Driving You," an organization backed by Uber's competitors in the taxi and limousine industry, which has fought the company's expansion.

Authorities identified Dalton as a 45-year-old from Kalamazoo Township who police said had no criminal record. They said victims of the shootings in and around the city of Kalamazoo had no apparent connection to him or to each other.

Uber spokeswoman Nairi Hourdajian confirmed Dalton had driven for Uber. Hourdajian wouldn't say whether he was picking up fares for the ride-sharing service Saturday night.

Authorities, however, were investigating a Facebook post which indicated the suspect was driving erratically around the time of the shootings and may have picked up at least one Uber fare while authorities were looking for him, according to Kalamazoo County Prosecutor Jeff Getting.

Uber said Sunday that it has offered to assist authorities in their investigation. In a statement, Uber chief security officer Joe Sullivan said the company is "horrified and heartbroken at the senseless violence."

While Uber says it screens drivers and conducts background checks, critics say the ride-hailing company uses private screening services that don't have access to as much information as local police can obtain when they check fingerprint records.

The company said earlier this month that it will pay $28.5 million to settle two lawsuits that alleged Uber misled customers about safety procedures and fees. It's also facing a separate a lawsuit by district attorneys in San Francisco and Los Angeles, who alleged that Uber's checks failed to prevent the company from hiring several felons.

If Dalton had no criminal record, it's not clear that Uber would have had any reason to keep him from driving. Uber, meanwhile, instituted a policy last year that prohibits driver and passengers from possessing firearms. Anyone found to be in violation of the policy may be prohibited from using or driving for the service.

While there have been several cases in which Uber drivers have been charged with assaulting passengers, there have also been incidents in which the company's drivers have been attacked by passengers.

Uber has also faced complaints that one of its executives in New York used information collected by the Uber app to track a passenger's movements. The company has since said that it has taken steps to protect passenger's privacy, including strict limits on access to the identities of riders.