The vehicular homicide trial of Jonathon Bales raised an interesting legal question that a defense attorney made his focus during opening arguments: At what point does a driver become impaired after smoking marijuana?

Deputy Spokane County Prosecutor Mary Ann Brady argued to the jury Monday that marijuana contributed to Bales’ turning some 47 feet prior to his intended intersection on Wandermere Road, causing the collision that killed 54-year-old Rene Blaume on July 16, 2010.

The lead investigator determined “the cause of the collision was because (Bales) had active THC in his blood at the time of the collision,” Brady said.

Blaume was driving 45 mph in the northbound lane and investigators estimated that Bales, 22, was driving a 1985 Pontiac Firebird 9 to 10 mph in the southbound lane when he crossed the centerline, causing the crash that severed Baume’s leg and killing her.

But defense attorney Sean Downs pointed out that none of the investigating deputies – who were trained to look for DUIs -- reported that Bales appeared to be impaired when they spoke to him after the crash. A blood was negative for alcohol but showed 3.9 nano-grams of active THC per milliliter. THC is the active ingredient in marijuana.

“That doesn’t mean anything unless there are signs of impairment,” Downs told the jury.  Bales “may have misjudged how far away Ms. Blaume’s scooter was … but that is a simple infraction.

“This was an incredibly tragic case to be sure. But the evidence will show it was nothing more than a terribly tragic accident.”

Brady called Rebecca Flaherty, a forensic toxicologist, who said the American Medical Association has yet to come to agreement – as they have with alcohol – which level drivers become impaired after smoking marijuana.

Downs asked Flaherty whether a blood test or the officers at the scene would be the best judge at determining impairment. She replied: “The officers are the scene.”

On re-direct, Brady asked Flaherty whether marijuana could have caused Bales to drive in the wrong lane and attempt to make a turn 47 feet before the intended intersection. “It could be an explanation for why he made those errors,” Flaherty responded.

The same issues caused a jury to become deadlocked last September.