The State Patrol is looking for witnesses to an accident on Highway 509 in Burien that left one man dead and three people seriously injured.

The State Patrol is looking for witnesses to an accident on Highway 509 in Burien that left one man dead and three people seriously hurt.

The accident occurred at 10:53 p.m. on Monday. Adam Knapp, 30, of Federal Way, was headed north on Highway 509 when he pulled over to the shoulder just south of South 128th Street, made a U-turn and drove into oncoming traffic, the State Patrol said.

His Subaru Legacy struck a Ford Explorer and all three women in the SUV were critically injured, police said. The Explorer then struck another car, according to police.

Knapp was killed when he climbed out of his vehicle and leapt across the highway barrier and was struck by four, and possibly five, vehicles.

One of the vehicles was an ambulance that had pulled over to help, the State Patrol said.

The State Patrol asks that anyone with information call Detective Stacy Moate at 425-401-7746.