Open this photo in gallery Peter Khill leaves the Hamilton courthouse with his then girlfriend, now wife Melinda Benko, in this file photo from June 11, 2018. Glenn Lowson/for The Globe and Mail

A former military reservist who shot and killed an Indigenous man in his rural Hamilton-area driveway four years ago must once again stand trial, Ontario’s Court of Appeal has ruled.

Though he was acquitted after a two-week trial in June, 2018, Peter Khill has been ordered to face a new trial for second-degree murder in the 2016 shooting death of Jonathan Styres, a 29-year-old father of two from Six Nations.

Mr. Khill, then 26, never denied that he killed Mr. Styres, who had been breaking into his pickup truck at the time of the fatal confrontation. But Mr. Khill had argued – successfully, at his trial – that he was acting in self defence.

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In a unanimous decision released Wednesday, the Court of Appeal has ruled that the trial judge had erred in his instructions to the jury, by failing to instruct them to consider the role of Mr. Khill’s conduct in the lead-up to the encounter, when assessing the reasonableness of the shooting.

“On this basis,” Justice David Doherty wrote, “the acquittal must be set aside and a new trial ordered.”

Mr. Khill had been asleep in bed with his girlfriend on Feb. 4, 2016, when he awoke around 3 a.m. to the sound of someone breaking into his pickup truck in the driveway. The then-26-year-old grabbed his shotgun from his bedroom closet, loaded it and headed to the driveway. There, he saw a man leaning into the passenger side of the pickup.

“Hey, hands up,” he yelled. When Mr. Styres turned toward him, arms rising, Mr. Khill fired. Mr. Styres died almost instantly.

At his trial, Mr. Khill told the jury that his actions were informed by the military training he’d received five years earlier as a reservist. There was a threat and he needed to “neutralize” it, he explained.

It took the jury six hours of deliberations to find Mr. Khill not guilty – a verdict that sparked shock and outrage in First Nations across the province.

“The verdict has left people feeling like it is open season for violence on Indigenous people,” Barb General, director of the Six Nations Justice Department, wrote in a Facebook post in July, 2018, after the Crown filed its appeal.

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The case also raised questions about the parameters of self defence.

As part of its appeal, the Crown had argued that the trial judge, Superior Court Justice Stephen Glithero, erred by failing to instruct the jury to consider the role that Mr. Khill had played in bringing about the confrontation.

In its decision Wednesday, the appeal court ruled that “Mr. Khill’s role in the incident leading up to the shooting was potentially a significant factor in the assessment of the reasonableness of the shooting. The failure to explain that relevance and to instruct the jury on the need to consider Mr. Khill’s conduct throughout the incident in assessing the reasonableness of the shooting left the jury unequipped to grapple with what may have been a crucial question in the evaluation of the reasonableness of Mr. Khill’s act.”

Lawyer Michael Lacy, who represented Mr. Khill in the appeal, said in an e-mail Wednesday that his client “has consistently maintained that he was acting in self-defence and was not guilty of any crime. We are carefully reviewing the Court’s decision and considering next steps including an application for leave to appeal to the Supreme Court of Canada.”

Lindsay Hill, the mother of Mr. Styres’s two daughters, said in an e-mail sent by her lawyer Wednesday that the news was a “step towards getting the justice we deserve.”

“Knowing that Jon’s killer could still be held accountable for his actions in which he took Jon’s life is an optimistic sign,” she said.

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“Although the order of a new trial is good news, it does not guarantee the accountability of Peter Khill’s actions. We must still continue this important call for reform and overhaul of the justice system in Canada.”