Uber says the man suspected of going on a western Michigan shooting rampage that left six people dead was one of its drivers.

But spokeswoman Nairi Hourdajian wouldn't say Sunday whether 45-year-old Jason Dalton was driving for the ride-sharing service Saturday night when the shootings occurred outside an apartment complex, car dealership and restaurant in and around Kalamazoo.

Uber Chief Security Officer Joe Sullivan says in a statement that the company is "horrified and heartbroken" and that Uber has offered assistance in the investigation.

Kalamazoo County Prosecutor Jeff Getting says authorities are investigating a Facebook post saying the suspect was an Uber driver driving erratically around the time of the shootings. He declined to elaborate.

Uber's firearms policy prohibits both drivers and passengers from carrying firearms in an Uber vehicle.