The outside of La Loche Community School is shown on Friday Jan. 22, 2016. A government source tells The Canadian Press at least two people have been killed in a mid-day shooting at a remote northern Saskatchewan school. THE CANADIAN PRESS/Joshua Mercredi

LA LOCHE, Sask. - As people in a remote Dene community try to fathom any possible motive for a mass shooting that took the lives of four people and wounded several others Friday, witnesses are recalling a terrifying scene of panic as students fled for their lives.

Noel Desjarlais-Thomas was just returning from lunch at the junior and senior high school in La Loche, Sask., when the shooter opened fire. In a flash, his friends were running past him, urging him to get out.

"Run, bro, run!" the 16-year-old said his friends shouted.

"There's a shotgun! There's a shotgun! They were just yelling to me. And then I was hearing those shots, too, so of course I started running."

The teen said it was a blur of partial sights and sounds. He thought he saw one of his friends fall to the ground after being shot, but wasn't sure.

"You know how it is — something happens, you've got to go for your life. I ended up running and I didn't want to look back."

Geordie Janvier, 16, was walking in the halls when the shots rang out.

"We were going back to gym class, that's when I heard the first shot," he explained. "I looked back. He didn't see me, that's why I ran to the gym class, closed the door, and I ran in the dressing room. We stayed there for, like, three hours."

Desjarlais-Thomas forwarded to The Canadian Press a screenshot of a chilling exchange that had taken place on social media a short time before the shooting between a young man and his friends.

"Just killed 2 ppl," wrote the young man. "Bout to shoot ip the school."

"Why?" asked a friend. "Why?"

Kevin Janvier said his 23-year old daughter, Marie, a teacher, was one of the victims.

RCMP told him the gunman is believed to have first shot two of his own siblings before killing Janvier’s daughter. He didn't know if the shooter personally knew his daughter.

"He shot two of his brothers at his home and made his way to the school," said Janvier, adding that Marie was his only child. "I'm just so sad."

RCMP confirmed at a brief news conference Friday night that the alleged shooter was in custody and they had investigators at both the school and a second location.

Speaking from Davos, Switzerland, a solemn Prime Minister Justin Trudeau said he had been advised of the situation by the commissioner of the RCMP.

"Obviously this is every parent's worst nightmare," the prime minister said. "We all grieve with and stand with the community of La Loche and all of Saskatchewan on this terrible, tragic day."

Bruce Heyman, the U.S. ambassador to Canada, sent a message of condolence and solidarity.

"We have experienced similar tragedies far too often in the United States and understand all too well the heartache and sadness that result from such a horrific event," he said.

Canadian tennis superstar Milos Raonic, competing at the Australian Open, dedicated his game victory to the people of La Loche.

"It was a difficult day back home ... I want to take a moment and give thoughts to that community, the families, the students and the school affected. Today's victory was for that community and a quick recovery. All of Canada and I'm sure the world is behind you."

Initially, the indication was five people had been killed but RCMP Chief Supt. Maureen Levy ended up revising that down to four at a news conference late Friday, adding that "a number" of others were injured.

She offered no further details.

"I can't give any information about their sex or their ages. We are in the early onset of the investigation and we want to ensure the integrity of the investigation."

Levy said one male was in custody, police had confiscated a firearm and there was no remaining risk to public safety. She said she was not aware of the threatening chat on social media.

The first reports of shots being fired at the high school came in at around 1 p.m. Mounties issued a warning to parents and residents to stay away, then locked down nearby Ducharme Elementary School as a precaution.

School co-ordinator Norma Janvier said she was in her office when she heard gunshots.

"I didn't know what was going on ... I thought the kids were just playing around or something, like a locker slamming and stuff," she told The Canadian Press.

She was going to check on the noise, but a teacher closed her office door, so Janvier stayed inside until she was told it was safe to leave.

"All I heard was cops running around in the school."

Saskatchewan Premier Wall promised that necessary crisis support and counselling services would be provided to the community of 3,000 on the eastern shore of Lac La Loche in the northern boreal forest.

Many residents of the small community hunt and fish to support their families. Desjarlais-Thomas said it is not the kind of place where kids would expect something so terrible.

"What I saw today was something un-ordinary," said the teen. "I just thought it was going to be a normal Friday and then, yeah, that happened."

Note to readers: This is a corrected story. An earlier version incorrectly identified Kevin Janvier as the acting mayor.

News from © The Canadian Press, 2016