BELLINGHAM, Wash. - A 22-year-old Montana man was walking along Interstate 5 at dawn on Saturday when he was hit and killed by a semi truck and a car, the Washington State Patrol reports.

Both vehicles left the scene after the accident, but the driver of the car returned later and talked to investigators.

Now state troopers are looking for the driver of the semi truck, which was the first to hit the man, identified as Michael S. Whitworth, 22, of Dillon, Mont.

Troopers said the impact probably caused damage to the front or side of the semi rig, possibly including the tires.

Troopers were called to the accident scene, in the northbound lanes of I-5 at Iowa Street in Bellingham, at about 4:30 a.m. Saturday.

The State Patrol reports that the pedestrian was walking in the roadway when he was struck and killed by the semi truck, then by the car as it was entering the freeway from the Iowa Street on-ramp.

"Our theory goes, that this person was hit by a semi first, then subsequently was struck by a second vehicle," said Trooper Keith Leary. "That person did return to the scene, and we do have that person's vehicle and have their statement."

The car, a 1999 Mercedes Benz, sustained minor damage. Its driver, a 24-year-old Bellingham man, returned to the scene with a friend and told troopers he thought he had hit an animal.

Leary said it's possible that the semi truck driver may not have realized that they struck a person.

"The person driving the semi may not have seen somebody, or even have known that they hit somebody," he said. "So we've got that information that were trying to look at, too."

He asked any semi driver who sees inexplicable damage to the front or side of their rig to contact the State Patrol at 360-658-2588. Anyone who witnessed the accident is also asked to call the State Patrol.