The man accused of causing the accident that killed twin sisters from Oak Harbor last Halloween was not driving while intoxicated, according to his attorney.

Toxicology results show that 53-year-old Ira Blackstock of Oak Harbor was “completely clean” at the time of the accident, Coupeville attorney Charles Arndt said this week.

Prosecutors charged Blackstock in Skagit County Superior Court Nov. 6 with two counts of vehicular homicide and one count of vehicular assault.

Janeah Goheen, a 17-year-old Oak Harbor resident, died at the scene of the Oct. 31, 2013 accident on Highway 20 near Anacortes; her twin sister, Janesah Goheen, was injured and passed away at Harborview Medical Center in Seattle.

Their friend, 18-year-old Alysha Pickler of Oak Harbor, suffered a concussion.

Detective Craig Cardinal with the Washington State Patrol told The Record in November that troopers found no indication that Blackstock was drinking prior to the crash, but his blood was drawn after field sobriety tests showed signs of possible impairment from medication or drugs.

Arndt said state patrol investigators are still looking into the cause of the accident. He said they’re trying to analyze a “black box” from the car that may have recorded his speed prior to the collision.

Skagit County Prosecutor Richard Weyrich did not return a call for comment.

Under Washington state law, there are three “prongs” to the vehicular homicide and vehicular assault charges.

Those prongs cover driving while impaired, driving in a reckless manner and driving with disregard for others. Each prong has different standard sentence ranges; the DUI-related version is the most serious.

Blackstock was charged under all alternatives of the charges.

According to Cardinal’s report on the accident, Blackstock was driving his 2006 Ford Mustang south on Highway 20 from “Sharpes Corner” in Skagit County and “accelerated rapidly” as he approached the intersection with Gibraltar Road.

The car, which had near-bald rear tires, broke traction on the wet asphalt, began to fishtail side-to-side and crossed into the oncoming lane.

The Mustang struck an oncoming 1993 Acura driven by Janesah Goheen just after 5 p.m.

“The purposeful and reckless acceleration by Ira L. Blackstock caused his Ford Mustang to strike the oncoming Acura four-door close to the northbound fog line of State Route no. 20,” Cardinal wrote.

Court records show that Blackstock was issued three speeding tickets in 2013.

Blackstock’s trial date was continued to April 14.