Ira Blackstock is guilty of causing a car crash on Halloween 2013 that killed 17-year-old twin sisters and badly injured their friend.

A jury in Skagit County Superior Court found the 54-year-old Oak Harbor man guilty of two counts of vehicular homicide and one count of vehicular assault today.

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

Their friend, Alysha Pickler, 18, of Oak Harbor, suffered a concussion and broken bones.

The trial lasted nearly two weeks and focused on expert testimony on the mechanics of the car and how Blackstock was driving in the moments before the impact.

Closing arguments started Thursday morning and continued until after lunch. The jury began deliberating just after 1 p.m.

Under the charges, Blackstock was accused of driving “in a reckless manner” or “with disregard for the safely of others.”

Skagit County Prosecutor Richard Weyrich argued that Blackstock was clearly reckless, from his choice in driving a Ford Mustang with bald tires to his decision to accelerate up to 85 mph on a wet road.

“This is the worst kind of tragedy,” he said. “This is a tragedy that could have been avoided if Mr. Blackstock had acted like a mature, responsible adult.”

Blackstock’s attorney, Charles Arndt of Coupeville, went after the prosecutor’s expert witnesses in his closing arguments. He questioned the testimony that pegged Blackstock’s speed prior to the accident; it was largely based on data collected from the car’s drivetrain control module.

He said a defense expert showed that it was physically impossible for the cars to have landed where they did if Blackstock was going at the speeds the prosecution alleged.

“One of the things the prosecution had difficulty doing is to fit their theory on a map,” he said.

He said control module data for speed is only accurate for a specific tire pressure, tire size and gear ratio; he said the prosecution failed to prove these factors.

Arndt suggested that prosecutors simply liked the conclusions the expert witnesses came up with and didn’t look any further.

“We’ll just show this number to the jury and we’ll show a bunch of gory pictures. Goodbye Mr. Blackstock,” he said of the prosecution’s trial strategy.

Arndt also focused on the data that showed the car’s throttle was at maximum even though the accelerator wasn’t pressed all the way down and that the throttle remained open all the way even after he let up on the gas pedal.

“Does anyone believe it’s reasonable and safe to have a car that over-responds when you press down on the accelerator and who cares when you let up?” he said.

He also pointed out that the National Highway Traffic Safety Administration collected more than 100 reports of unexplained acceleration in Ford Mustangs.

Deputy Prosecutor Russell Brown finished up closing arguments. He said Blackstock was driving a “souped up sports car” that was designed to go fast and witnesses confirmed that he accelerated quickly before the crash.

He pointed out that Blackstock only let up a little on the accelerator before the accident; he said it was still depressed by nearly 70 percent.

“There is zero reason you would drive a car that fast unless you are completely indifferent (to others),” he said.