A driver who struck and killed a Snoqualmie man, then drove into a ditch along Interstate 90 between Preston and S.R. 18 Tuesday night has been booked into the King County Jail on suspicion of driving under the influence. State Patrolmen are investigating the incident as a possible vehicular homicide.

Washington State Trooper Rick Johnson said Wednesday that the victim, Robert Thompson, was assisting his girlfriend and her daughter, who had car troubles and were pulled over to the shoulder of the westbound lanes of I-90 at around 11 p.m. the night of June 20. Thompson, 47, of Snoqualmie, was trying to hook a tow chain to the woman’s vehicle when a westbound Nissan Frontier pickup truck drifted into the shoulder and struck the woman’s car and Thompson.

The driver of the pickup truck continued past the collision, but apparently lost control of the vehicle and drove into a ditch after a few hundred feet, Johnson added.

Troopers were called to the scene at 11:20 p.m. They determined that Thompson had died in the collision. The two women in the vehicle were not injured, but were transported to Overlake Medical Center as a precaution. The driver of the pickup truck was also not injured.

Police arrested the driver under investigation of vehicular homicide. The driver’s blood was sent to a toxicology lab to test it for evidence of intoxication.