Warning: Disturbing content

NEW WESTMINSTER, B.C. - The principal of Abbotsford Senior Secondary School says he was in a meeting in his office around 2 p.m. on Nov. 1, 2016 when the secretaries all stood up and screamed.

Robert Comeau took the stand at the trial of the man accused of fatally stabbing 13-year-old Letisha Reimer at the school that day, and seriously wounding another student.

Gabriel Klein has pleaded not guilty to second-degree murder and aggravated assault.

The Crown said it's not being disputed that Klein was the person responsible, but he intends to raise the defence of not criminally responsible due to a mental disorder.

Comeau told the court Tuesday one secretary said there was a fight happening. Another said "he has a knife."

He testified the office windows looked out into the school's rotunda, where the attack took place.

Comeau testified he ran out, along with the two vice-principals, and saw a female victim on the ground and a man overtop of her with a knife.

"He was stabbing her," Comeau said. He told the court the man had the victim pinned to the ground and had the knife above his head.

Comeau testified the man made eye contact with him, dropped the knife and got up and backed away.

The principal said he told the man first to sit in a chair, then kneel face-down on the floor with his hands behind his back, and the man complied. Comeau testified he and a vice-principal held onto the man, and said he appeared to struggle for a bit, but then seemed to give up.

Comeau said he left the vice-principal with the man and initiated the school's lockdown procedure, which involves hitting a button that sounds a siren. Students are then to enter the closest classroom.

He says teachers are to lock the classroom doors and then everyone inside stays quiet and out of sight of the hallway.

Comeau testified when he returned to the man, he searched him, only finding a piece of paper in one of his pockets which he threw into a corner.

Comeau told the court the victim on the floor was losing a lot of blood, and staff members were administering first aid. He testified he didn't recognize her at first, but was later told it was Reimer.

Comeau testified a student in the computer lab said there was another victim, so he went in there to find a teacher helping the student. He told the court she had been stabbed, and there was blood everywhere. He testified he asked her if she knew the suspect, or knew why this happened, and she said no.

During cross examination, Comeau told the court the man had a blank facial expression while looking in the direction of Reimer.

Now-retired vice-principal Bruce Cuthbertson also testified, his voice breaking with emotion several times. He told the court he saw a girl fall to the ground, with a man holding onto her, and as she fell the man attacked her, in an assault that continued when she was on the ground.

Cuthbertson testified the man stopped as they approached, and he heard the sound of a metal object hitting the floor. He said the man was breathing heavily, but showed no emotion.

Cuthbertson told the court he held onto the man until police arrived, using a "control position" he knew from teaching wrestling. He testified he watched as staff tried to help the victim, and heard a school counsellor begging her to stay alive, but the blood kept coming.

"...it became evident to me that I was holding on to someone who had killed someone," Cuthbertson said.

The court also heard from Audrey Faber, a woman who testified she saw a man who seemed "quite agitated" on Marshall Road around 1:30 p.m. the day of the stabbings.

Faber testified the man was clenching his hands, making guttural, growling noises, and appeared to be walking on the balls of his feet. She told the court she called 911 and was told someone would come and check it out.

There was also testimony from Crystal Andresen, who was an employee at outdoor sporting goods store Cabela's on Nov. 1, 2016.

She testified around 12:15 p.m. a male customer asked her where the knives where located, and she showed him. She told the court it was a normal interaction and she did not keep an eye on him.

In its opening statement, the Crown said Klein went to a Cabela's just after noon on the day of the attacks, where it maintains he stole a hunting-style knife used in the stabbings.

Witnesses have testified Klein went to Abbotsford Regional Hospital a few days before the attacks, and was directed to a homeless shelter where he spent the next few nights.

The court heard testimony from multiple witnesses that Klein said he wanted to return home to Alberta and wanted to talk to his mother.

Staff at the homeless shelter testified on the morning of Nov. 1, Klein became upset when he could not call his mother or get a bus ticket right away, and left.

A staff member at the shelter also testified that on Oct. 31 she gave Klein directions to the public library which was attached to the school at the time, so he could use a computer to email his family.

Comeau testified a wall has now been put in place dividing the school from the public library on the inside.

CTV News Vancouver's Maria Weisgarber is in court. Follow along live.