When Evan Todd crossed paths with Eric Harris and Dylan Klebold in the school hallway, he had no idea what horrors the pair had already planned for Columbine High.
Weeks later, Eric and Dylan would have a gun pointed at Evan's head, forcing him to beg for his life, according to news.com.au.
When Evan talks about the hallway exchange to news.com.au over the phone from Littleton, Colorado, he pauses. At one moment, he takes a small break.
"The moment in the hallway, when I look back on it through the lens of time and see what had happened weeks later, they almost had a smirk on their face. I don't know why I remember that exchange, but it was a knowing look.
"I walked past them, they saw me and I saw them. I'd never talked to them, ever had a class with them."
As we edge closer to the 20-year anniversary of the Columbine High School massacre, where 13 people were killed and a further 24 injured in a complex plot that involved fire bombs and explosive devices, Evan still doesn't know why Eric and Dylan spared his life.
But it was this very moment that led him to the belief that teachers should have the ability to carry guns in schools.
The school shooting on April 20, 1999 shocked the world, not only because it was a world unfamiliar with school shootings at the time, but the tortuous way in which the high school seniors killed their victims.
The shooting was already in full swing by the time the pair entered the library, where Evan, then a 15-year-old sophomore, was finishing last-minute edits on an English report that was due that day.
Eric appeared at the doorway, telling the 56 people inside to "get up". He was holding a shotgun. Evan scattered towards a desk to hide.
Eric yelled, shooting twice in the direction of Evan's desk. He was hit in the lower back before moving to hide behind an administrative counter. Eric fired more shots towards Evan's head, blowing shrapnel into his face.
Evan survived and he hid, frozen, for several more minutes while Eric and Dylan murdered his classmates at random, taunting them with each shot.
"They yelled certain things and then they started walking around firing at random, and asking people questions and basically shooting execution style," Evan said.
He remembers the screams, the shots. He remembers Eric and Dylan getting bored and considering "knifing people" instead. He remembers how they shot 18-year-old athlete Isaiah Shoels and their jokes over the gun splatter.
As Cassie Bernall lay hiding under a row of computers, Eric knelt towards her and said "peek-a-boo" before shooting her in the head.
"They were having a good time, which is disgusting, but it's the only way to put it," Evan said.
He prayed silently to himself: "Please God, let me live."
Eric and Dylan made their way around the room, up and down the aisles in a clockwise pattern until they made their way to where Evan was hiding towards the front of the library.
Dylan pulled out a chair and found him. He put a gun to his head.
"Why shouldn't I kill you?" he asked.
"I don't want any trouble," Evan replied.
Dylan moved closer towards Evan's face. He remembers the look in his eyes.
"It was a look that I'd never seen before or since that day, Dylan was really wide-eyed and demonic and hollow and cold. There was just death in his eyes."
Dylan replied to Evan: "Trouble? You don't know what f***ing trouble is."
"That's not what I mean. I've been good to you and everyone at the school and you know it,'" Evan said.
Dylan paused, and turned to Eric. "You can kill him if you want."
Eric looked at Evan. Then looked at Dylan.
"Eric said, 'Let's go to the Commons,' and they started to leave," Evan said.
Dylan's facial expression changed. He looked "pissed off".
"I honestly don't know why I said what I did, it just came out. Even when I said I didn't want any trouble, I was basically pleading for my life.
"Somehow those were the words that let me live.
"I really do believe that something greater happened in that moment, call it divine intervention or however you want to explain it. Something happened in that moment, and it was over."
The room was filled with smoke, Evan remembers seeing pools of blood everywhere, motionless bodies.
Evan escaped with his life, but he still doesn't know why.
Thirteen people didn't make it out of Columbine High School alive that day, and after years of deliberating, he's come to the conclusion that teachers should be allowed to carry guns in school as a preventive measure.
"I did have a period after Columbine where I greatly questioned whether guns were the problem. I really truly wanted to find some kind of answer to what happened, some kind of way to help prevent it," he said.
"I looked at all the angles and I guess I don't think guns are the issue. I look at my upbringing, all my friends, we had more access to guns than Eric and Dylan and we didn't murder any body. They didn't have any guns in their homes whereas I was raised with guns.
"I could have gotten a gun from my household or a friend's household that was hanging on the wall, but we never did. It never even crossed my mind."
Evan doesn't believe teachers should be forced to carry a gun, but if they already carry a concealed-weapons permit, why not use the opportunity to use it in a school shooting scenario?
"There are many organisations and law enforcement agencies who have offered free tactical training to these teachers free of charge and people are willing to do it.
"That's the part that boggles my mind, that people are stopping people from protecting themselves, it boggles my mind."
Evan says he isn't alone in his views, either.
"There's a good group of people from Columbine and other shootings who agree with me, but I think a lot of times people were silenced just out of shame from the media in America because it wasn't acceptable to say."
In February, Axios reported that since Columbine, there have been 10 US school shootings where four or more people had been killed, accounting for a total of 122 deaths.