A judge has declared a mistrial in the case of a man charged with a drinking-and-driving offence. ((CBC))

A Saskatoon judge has declared a mistrial in a drunk-driving case where the arresting officer had a history that was not disclosed.

The case dates back to April when Darren Usselman was charged with having a blood-alcohol level over .08 while operating his truck.

The provincial court case went to trial in June. RCMP officer Sgt. Warren Gherasim, who did the roadside test, was the Crown's main witness.

Usselman was found guilty, but then defence lawyer Ron Piche stumbled across Gherasim's background.

"It was learned that the sole witness, the main investigating officer, was himself the subject of disciplinary proceedings, professional standards and the like, in connection with an allegation of having consumed alcohol and driven his vehicle and being in an accident," Piche said.

Gherasim had been sanctioned in 2006 for disgraceful conduct after rolling his vehicle while off-duty.

He admitted at an internal hearing that he had been drinking, but he was never charged. He was suspended without pay for eight days.

A Supreme Court ruling in 2009 said that police must tell the Crown about any misconduct records which may have a bearing on a case. 

Under disclosure rules, the Crown would then be required to disclose this information to the defence.

Before Usselman could be sentenced, Judge Marilyn Gray declared a mistrial.

In her written decision she said, "Here the officer had been disciplined for the very conduct of which Mr. Usselman had been accused."

Piche said it would've come up in cross examination, had he known.

"It may have influenced the result of the case, obviously, because credibility is always an issue, not only with civilians but police witnesses as well," he said.

No date has been set for the new trial.