Santa Rosa police were trying to unravel the mystery Saturday of an unconscious man found lying in the roadway on Friday night.

The man described as being in his 60s was found at 9 p.m. Friday in the 1400 block of Peterson Lane, near Guerneville Road.

He had sustained a life-threatening head injury and was lying partially in the west side of the street.

Police were unable to question the man, whose name they have not disclosed. And they did not know if he was hit by a passing car or injured in some kind of attack.

Police Sgt. Brad Conners said traffic investigators and detectives from the violent crimes unit were looking into the matter.

"We're still trying to figure out if it is a traffic collision or an assault," Conners said. "We really don't know what happened."

The man was taken to a hospital, Sgt. Dave Linscomb said. An update of his condition was not available.

Linscomb said the man had apparently left his nearby home to walk to the store.

Police closed a section of Peterson Road until about 2:45 a.m. Saturday to investigate.

A white car occupied by two males was reportedly seen in the area at the time of the incident, Linscomb said.

The car reportedly had a loud exhaust. Conners said it is unknown if the car is connected to the injured man.

"We're looking for someone to come forward with some information so we can start putting it together,"" Conners said.

Anyone with information is asked to call police at 543-3600.Anyone with information is asked to call police at 543-3600.