NEW WESTMINSTER, B.C. - A B.C. Supreme Court judge has reserved her decision in the trial of a man accused of gunning down a police officer in Abbotsford, B.C.

Justice Carol Ross warned Crown and defence lawyers on Friday that if she concludes Oscar Arfmann was the man who killed Const. John Davidson, she wants to hear from each side about the potential role of his mental state.

"I remain of the view that there are potentially outstanding issues relating to his mental status at the time of the offence," Ross told counsel.

"I'm alerting you so that if or when we reach that point and I raise it, you won't be taken by surprise but will have thought through your positions."

Ross said it's also possible she'll find Arfmann not guilty of the murder of Davidson, who was responding to reports of a stolen vehicle when he was killed in November 2017.

The trial by judge alone has been adjourned until Sept. 25 when Ross will set a date to release her decision.

Closing arguments in the first-degree murder trial ended with defence lawyers arguing that Arfmann had no motive to kill Davidson and that the Crown's case depended on conflicting witness accounts.

The prosecution has argued Arfmann ambushed the 53-year-old officer as he got out of his vehicle, shooting him twice from behind.

Crown attorney Wendy Stephen told the trial this week that a man matching Arfmann's description stole a vehicle two days earlier and shot at the dealership managers who confronted him, left the area briefly, then returned and killed Davidson to escape arrest.

Witnesses at the trial identified a black Mustang and man wearing a black leather jacket with a gun at the scene of the shooting, and that proves he's guilty, Stephen said.

But the defence said only two eye witnesses say they saw the shooting and their descriptions of the suspect vary.

"There is not a single witness who can say, 'It was Mr. Arfmann who did it,' " said lawyer Frances Mahon, who is part of the legal team defending Arfmann.

Mahon also questioned the Crown's assertion that the rifle accepted as the murder weapon was linked to the accused.

Arfmann's DNA was found only on a small area of the gun and, since he was bleeding profusely at the time of his arrest, it's possible that DNA was transferred by an officer at the scene, she said.

None of Davidson's blood was found on Arfmann, nor was Arfmann's DNA confirmed on bullet casings found at the scene, Mahon said.

"The Crown's case is really only as strong as the foundation it rests on," she told the court. "We say it is not so solid as it appears at first glance."

Speaking outside the court, defence lawyer Martin Peters said the judge's request for positions on Arfmann's mental state means that if his client is found guilty, the court would next explore the question of whether he can be held criminally responsible for the murder.

"That would depend upon essentially a trial of that issue, of what was his mental state at the time, what do doctors say about it," Peters said.

He acknowledged that the Crown has a strong case, given that Arfmann has been confirmed at locations minutes before and after the shooting. There is only about one minute - during the time Davidson was shot - that Arfmann is not accounted for, except by two eyewitness accounts that have varying suspect descriptions, Peters said.

"The Crown's argument is, it really can't be anybody else. So that's what we're up against."

Still, he said the prosecution has failed to prove beyond a reasonable doubt that Arfmann is guilty.

Abbotsford police Chief Mike Serr said that Friday was a difficult day for Davidson's family members, who have attended every day of the hearing.

"Certainly, today there were some tough moments, hearing the arguments of the defence. But we explained the process and how important that is to our justice system that (defendants) be afforded good counsel," Serr said outside the court.

He commended the officers who responded to the shooting, the investigators and the Crown prosecutors.

"I'm very confident with the case that's been presented and we'll leave it with the court now to render a decision."