Gerald Stanley told the jury at his second-degree murder trial in Saskatchewan on Monday he didn't follow typical firearm safety measures before Colten Boushie was fatally shot because he thought his handgun was out of bullets.

"When it's empty, it's just a piece of metal," Stanley testified in Court of Queen's Bench, in the community of Battleford.

"Unless it blows somebody in the head," replied senior Crown Prosecutor Bill Burge.

These and other details of the day Boushie died in Stanley's Saskatchewan farmyard emerged during Burge's cross-examination on Monday afternoon.

The farmer was charged after Boushie, 22, was shot during an altercation between Stanley's family and group of young people from the Red Pheasant Cree Nation reserve who had driven onto his rural property in a grey SUV on Aug. 9, 2016. Stanley, 56, has pleaded not guilty.

Earlier Monday afternoon, Stanley first answered questions from his lawyer, Scott Spencer about events from the afternoon of Aug. 9, 2016.

'The thing just went off'

Stanley repeatedly told the jury he didn't mean to shoot Boushie.

"Boom, the thing just went off," Stanley said.

He said he was fixing a fence with his son, Sheldon, 28, while his wife mowed the lawn. A vehicle drove into the yard. Its occupants appeared to be attempting to steal a quad ATV.

The RCMP took this photo of an ATV on Stanley's property. (RCMP)

When they heard Sheldon yelling, the people got back in the car and reversed toward Stanley. Stanley said he kicked the tail light. The vehicle then drove forward, revving fast, toward Sheldon, who hit the windshield with a hammer. The vehicle then rammed into one of the Stanley family's unoccupied SUV vehicles.

Stanley said Sheldon then ran off. By this point, Stanley said he was afraid, thinking of the news reports of cars crashing into crowds and a double murder that occurred 15 kilometres from his farm yard.

"I was still in disbelief about what was going on here," Stanley testified.

As far as I was concerned, it was empty — it had fired its last shot. - Gerald Stanley

He said he walked to his shed, grabbed a handgun and loaded it. When he came out of the shed, he saw two males outside the grey SUV.

Stanley said he heard two loud sounds as he aimed skyward and pulled the trigger two or three times. The two males fled, he said. Stanley said he lowered the gun and checked to ensure it was disabled.

"As far as I was concerned, it was empty — it had fired its last shot," Stanley testified.

He said he then realized he couldn't see his wife, and had a feeling of "pure terror" fearing she'd been pinned under the grey SUV.

Stanley said he was going to look under the vehicle, but popped back up after it started revving again.

"I wanted that car off," he said.

Stanley said he reached for the keys with one hand, with the handgun in the other. Then the gun fired.

The RCMP took this photo of the semi-automatic pistol that is believed to have killed Colten Boushie. (RCMP)

Stanley said he didn't mean to kill or even hurt anyone.

"I just wanted them to leave," he said, adding he didn't pull the trigger.

Stanley said he learned later that there was a firearm in the grey SUV, but he didn't see it or know about it at the time of the shooting.

'Wasn't thinking straight'

Following the afternoon break, Stanley's lawyer continued his questioning, followed by a cross-examination by Burge.

Burge asked Stanley about firearm safety. Stanley said he is licensed to own restricted firearms and has taken safety courses.

"Did you learn not to point a gun at somebody?" Burge asked. Stanley replied, "yes."

Stanley said he believed there were only two bullets in the gun, but under questioning from Burge said he "wasn't 100 per cent sure."

Stanley said again that he reached for the keys with one hand and the gun, in the other hand, went off inside the vehicle.

"I didn't even realize I did have [the gun] inside," he said.

Burge asked Stanley why he didn't drop or set down the gun before reaching in to the car.

"I just wasn't thinking straight," Stanley said.

Stanley repeatedly said he didn't pull the trigger.

"You sure?" Burge said.

"Yeah," Stanley replied.

An aerial view of Gerald Stanley's farm taken by RCMP. (RCMP)

The mood was tense throughout the day. Several people left the courtroom during the more graphic portions of the testimony or when Stanley was asked to re-enact scenes holding the handgun. After court adjourned late in the afternoon, a group of supporters held up signs and chanted "Justice for Colten" as they have on previous occasions. Boushie's cousin, Jade Tootoosis, said watching Stanley testify was "one of the hardest things I've ever seen."

The trial is in its second week in Battleford, about 130 kilometres northwest of Saskatoon. The jury has been told they can go home until Thursday morning while lawyers and Justice Martel Popescul discuss legal issues and craft their final statements.

Ultimately, this comes down to a freak accident. - Scott Spencer, defence lawyer

Monday morning, Spencer had informed the jury in his opening statement that Stanley was going to testify.

"No games. Gerry's going to testify. He has to," Spencer said.

"Ultimately, this comes down to a freak accident that came about over the course of an unimaginably scary situation."

According to Spencer, Stanley was intending to fire warning shots. He referred to the phenomenon of "hang fire," in which a firearm will delay firing of a bullet.

"You have to look at it from Gerry's perspective ... the fear of the unknown," Spencer told the jury.

Sheldon Stanley, the son of Gerald Stanley, testified as a Crown witness last week. (Chanss Lagaden/CBC)

Spencer said members of the Stanley family were working that day on their farm and were not "looking for trouble" when the grey SUV pulled into the farm driveway.

Stanley didn't have the luxury of waiting for police to arrive on his isolated farm, his lawyer said.

"For farm people, your yard is your castle. That's part of the story here," Spencer said.

Spencer said the case is about protecting people from harm.

"Colten Boushie's death is a tragedy ... it is never right to take someone's life over property, but that's not what this case is about," Spencer said.

He said there was a rifle between Boushie's legs pointing at Stanley, but the farmer "wasn't aware of that."

"This wasn't about using lethal force to repel a threat," Spencer told the jury.