A Winnipeg RCMP officer whose gun was stolen from his police truck and used a short time later to shoot and seriously injure 16-year-old Calli Vanderaa told a judge Friday he could not explain why he didn't bring the gun into his house that night.

"To this day, I have no defence," Sgt. Christopher McCuen told Justice Sheldon Lanchberry. "I have no idea why I did that."

Vanderaa was shot Oct. 24, 2015 while sitting in a car outside an Autumnwood Drive convenience store.

Matthew McKay, 24, is on trial charged with attempted murder and 10 firearm offences.

Prosecutors allege McKay and another man stole the loaded handgun and other items from the truck while attending a party hosted by McCuen's son in the garage of his Sage Creek home.

McCuen, a collision reconstructionist, said he had been called out early that morning to an accident scene in Gimli, Man. and returned home around 3 p.m., driving his truck onto a parking pad adjacent to the garage.

McCuen said he left his duty belt — which held his handgun, pepper spray, handcuffs and ammunition magazines — inside a bin sitting between the front seats before going into the house.

The bin "is for paper and files," he said. "I don't know why I decided to put it in there at that time."

Unaware of party in the garage

McCuen said he slept for a couple of hours, had dinner and spent the rest of the night in the basement watching television. He said he was unaware of the party in the garage.

When he got up the next morning, he stepped on something wet in the kitchen and after a conversation with his wife went to check out the garage, McCuen told court.

"I opened the door and saw a significant number of chairs in a semi-circle," he said. "Sitting on one of the chairs was a computer from my truck."

A backpack which McCuen kept in the truck and used to store his work cameras was also in the garage. One of the cameras was missing, he said. McCuen looked around the garage and found his duty belt, empty.

"It was clear to me that someone ... had gone through my truck," he said.

McCuen went to his truck, "hoping against hope" that his gun had fallen out of the duty belt and was still in the front seat bin, "but it wasn't there," he said.

After confronting his son, McCuen called his supervisor to see what he should do next.

Did not answer all of WPS' questions

"It was decided I would make the call to 911 and take it from there," he said.

When later interviewed by the Winnipeg Police Service's major crimes unit, McCuen did not answer all their questions, he told court.

"My lawyer explained that I might be facing some jeopardy because of how I left the firearm in the vehicle," he said.

McCuen was not asked whether he had locked the truck before going into the house for the night.

MCuen said it was his normal practice to keep his firearm in the house at night, safely stored in a regulation container.

Defence lawyer Todd Bourcier suggested McCuen was in the habit of unsafely storing his gun, arguing it would have taken less effort to walk to the house with his duty belt on than remove it and place it inside the front seat bin.

"So the only time you improperly stored your firearm in your vehicle was the night it was stolen?" Bourcier said.

"That's right," McCuen said.