Detectives believe that 45-year-old Jason Dalton shot eight people - six of them fatally - in various locations around Kalamazoo.
Uber confirmed to Business Insider that Dalton was a driver who had passed his background check.
A Facebook post by a Kalamazoo resident written on Saturday and screenshotted by WoodTV says that her fiance's Uber driverf, named Jason, was driving very erratically: sideswiping another car, swerving in and out of oncoming traffic, speeding, and refusing to pull over.
"The Uber driver named JASON drives a silver Chevy Equinox is NOT a safe ride," Mackenzie Waite wrote on Facebook.
Uber is helping police with the investigation.
"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 are reaching out to the police to help with their investigation in any way that we can."
Dalton is currently in police custody and no motive has yet been determined for this crime.
Business Insider reached out to Uber for additional comment.