A man seen walking alongside Interstate 8 in Mission Valley Friday morning was found dead minutes later under suspicious and mysterious circumstances, authorities reported.

SAN DIEGO (CNS) - A man seen walking alongside Interstate 8 in Mission Valley Friday morning was found dead minutes later under suspicious and mysterious circumstances, authorities reported.

The California Highway Patrol began receiving calls about the pedestrian, who appeared to be in his mid-30s, on the north side of the freeway near the I-805 interchange shortly before 6:30 a.m., according to San Diego police.

About 10 minutes later, a 911 caller notified the California Highway Patrol that the man was lying on the roadside.

Officers arrived to find the pedestrian fatally injured, with trauma of unknown origin to the back of his head, SDPD Lt. Ray Valentin said. Medics pronounced the victim dead at the scene.

Authorities closed the three right-hand westbound lanes of the freeway around the site of the fatality while investigators gathered evidence.

The man, who may have been homeless, did not appear to have been shot or hit by a car, Valentin told reporters.

Detectives were looking into a reported sighting of a white BMW sedan parked near the victim with a man standing next to it at about the time the body was spotted, according to Valentin. It was unclear if that person was related to the fatality, the lieutenant said.

The county Medical Examiner's Office will determine the victim's cause of death and seek to identify him.