A crucial piece of evidence in the Crown's case against an off-duty RCMP officer involved in a fatal motorcycle accident will be included as evidence in his obstruction of justice trial, in part because it's in the public interest, a B.C. Supreme Court judge has ruled.

Judge Janice Dillon decided Thursday in favour of admitting statements made to a Delta, B.C. police officer by Cpl. Monty Robinson that he downed two shots of vodka to "calm his nerves" after leaving the crash scene.

Const. Sarah Swallow arrested the man after the October 2008 crash that killed a 21-year-old motorcyclist.

Robinson's lawyer had argued his client wasn't notified of his right to a lawyer before he spoke to the officer.

Robinson is facing the high-profile accusations in the wake of scrutiny over his role as the senior officer among four Mounties who were at Vancouver's airport when Polish immigrant Robert Dziekanski died after being zapped by an RCMP Taser.

The allegations being considered in this trial equate to a potentially serious offence involving a police officer, Dillon said while reading her oral judgment from the bench.

"The public interest in having this case adjudicated on its merits is high," she said. "The repute of the justice system would suffer if this evidence was not admitted."

Swallow did not know Robinson was a 12-year RCMP veteran working in Richmond, south of Vancouver, when she arrived on the scene of the collision between the man's car and a motorcycle.

She learned from a man walking his dog that the driver had handed him his licence and left to take his children home immediately following the crash.

A few minutes later, she spotted a man inspecting the wreckage and he identified himself as the driver she was looking for.

Swallow appeared concerned about Robinson's well-being and did not take an adversarial approach as she asked him about what happened and guided him away from the carnage, the judge said.

Swallow, a constable with 15-months experience, did notice the man was at times slurring his words and walking with deliberate steps. She said the effects appeared greater than might be expected from two shots in the ten minutes prior.

"(Robinson was a) very experienced police officer who would have known the nature of Swallow's duties in this situation, along with his rights under the law," Dillon said.

Robinson sat in the back seat of Swallow's police car with the door open and his feet on the road as the two spoke. She re-assured him that his children, who complained of pain after the crash, were being tended to.

When her suspicions grew strong that the man was impaired, she "promptly and properly" advised him of his rights in making his arrest.

"The line at which this interaction became a detention is blurred, and the officer's mistake, if there was one, is understandable," Dillon said. "This is not serious police misconduct."

Robinson only informed Swallow that he, too, was a police officer when he was later being booked at the station.

The judge noted that Robinson took an RCMP data training course in 2005 where he was taught that people can defeat an impaired charge if they have another drink after the accident.

"The statement that he had consumed two shots of vodka after driving was exculpatory in nature, perhaps purposefully intended to divert an arrest for impaired driving," said the judge.

She said his policing experience makes it difficult to say if his right to make a choice about speaking with Swallow was undermined.

Outside court, the mother of 21-year-old Orion Hutchison, the motorcyclist killed in the collision with Robinson's Jeep, said she was so relieved by the ruling, she was shaking.

"This case is not only important to us personally, for obvious reasons, but to the general public," she said, "just with regard to retaining or restoring some kind of faith in our justice system."