OPP Const. Brian Bellefeuille's character is an essential element in his trial for assault on a First Nations man, according to arguments made by the Crown attorney in court on Monday.

Bellefeuille was charged after an altercation with Gary Megan in a Geraldton jail cell last February. Megan suffered a head injury.

"His credibility is the issue in this case," Andrew Cappell told Justice F.A. Sargent in requesting permission to ask Bellefeuille about his reputation.

But the judge disagreed.

"He hasn't put his reputation at issue," Justice Sargent said to Cappell. "And if you want to have a nice talk with the Court of Appeal appeal, you go ahead, sir."

It was one of many heated interactions between Cappell and Sargent in a full day of testimony.

Sargent cut off Cappell's questioning of Bellefeuille about the reasons the officer arrested Megan for public intoxication outside the bar in Geraldton.

"My grounds for arrest were safety," Bellefeuille said, explaining he was worried that Megan was planning to walk more than 50 km home to Aroland First Nation. "I can't gamble with this stuff. I'd already be in jail for neglect of duty."

When Cappell attempted to question Bellefeuille about his belief Megan would walk home, the judge sided with a defence objection.

"So, I'm not allowed to ask more questions about this?" Cappell asked, throwing up his hands.

"That is exactly right," Sargent said.

Cappell also sparred with Bellefeuille, having difficulty getting him to agree with him on anything.

"There can only be one true version of a story, right?" Cappell asked at one point.

"That's kind of a loaded question," Bellefeuille responded.

Like many witnesses, Bellefeuille was shown a surveillance video from the bar on the night of the arrest. Notes he took in his police notebook indicate that Megan required assistance to get to the cruiser after Bellefeuille arrested him. But Megan walks on his own in the video.

"Was [the mistake in the notebook] an attempt to make it look like Mr. Megan was more intoxicated than he was?" Cappell asked Bellefeuille.

"It was an oversight," Bellefeuille said. "I don't lie."

The judge also issued his opinion that he doesn't believe Megan's arrest was 'targeted'. Cappell is attempting to link it to an incident earlier that day when Megan made an obscene gesture to another OPP officer.

"I just don't buy it," Sargent said.

Bellefeuille will be on the stand again on Tuesday. That's when the Crown expects to finish the cross-examination. Both lawyers said they're prepared to make closing submissions in the case as well on Tuesday.