B.C.'s highest court has overturned a murder conviction and ordered a new trial for a man who claims his handgun went off accidentally when he killed a teenager at a Kelowna house party.

Trevor Shannon was convicted by a jury of second-degree murder in the slaying of 18-year-old Evan Wilkes, who was killed by a single shot to the head on April 7, 2007.

The B.C. Court of Appeal ruled Monday that the judge in Shannon's 2008 trial didn't properly clarify a question from the jury about the intent required for a second-degree murder conviction. The three-member panel ruled that Shannon's conviction should be set aside to make way for a new trial on the same charge.

Shannon, a landscaper with a side business as a drug dealer, was high on marijuana and possibly other drugs when he arrived at a house party full of young people on the night of the killing, according to court documents.

At some point during the night, Shannon saw that two of his friends were surrounded by an angry crowd of people, some pointing bear spray and kitchen knives.

Shannon testified during his trial that he grabbed a handgun from the waist of his pants, waved it around and yelled at the crowd to back away from his friends. Then the three of them left the house and headed for their vehicle.

But once Shannon was in the driveway, he said that he was confronted by Wilkes. Some of his fellow partygoers testified that Wilkes was drunk and taunting Shannon.

"He was calling me extremely rude names, and he was asking me to shoot him, and he didn't -- he didn't think the gun was real," Shannon said.

"He was extremely aggressive with me, with his actions and with his words."

He said that he saw Wilkes turning to the person standing beside him, and he believed that he was reaching for a can of bear spray.

"I took a step forward, and I hit him in the side of the head with the gun," Shannon told the court. "The only thing I know is I -- I was trying to hit him with the metal of the gun, that's all I know, just like the side."

But instead of just hitting the younger man, Shannon also pulled the trigger, shattering Wilkes' skull with the bullet and sending bone fragments into his brain. When he realized what he had done, he ran to a nearby beach, buried the gun under a dock and threw the remaining bullets into the lake.

Shannon was arrested a few minutes later on a nearby street.

During Shannon's trial, his lawyers argued that Shannon hit Wilkes with his gun in self-defence and that pulling the trigger was an accident. They will have a chance to make their case again when Shannon's next trial begins.