After walking past the fifth body sprawled across a Yonge Street sidewalk on April 23, 2018, TTC Special Constable Bill Perivolaris knew he was responding to a massive casualty event.

Perivolaris and his partner Angela Johnston were responding to a red alarm on a TTC bus in North York when they arrived on the scene of what would later be known as a deadly van attack. A minute and a half earlier, a vehicle had jumped a curb and struck a number of pedestrians along a portion of Yonge Street.

“We knew that something tragic had happened based on the nature of the call that we got,” Perivolaris told CTV News Toronto. “The dispatcher told us there was yelling and screaming on the bus and so it was a very serious call that had come in.”

“At the time that the call came in, we didn’t realize it was on the sidewalk.”

The TTC constables arrived at the scene and blocked off the street with their vehicle. That’s when they saw the bodies lying on the ground.

“I remember it being pretty chaotic,” Johnston said. “There were a lot of people clearly stressed and crying for help and there were clearly people injured and some that were already deceased.”

As Johnston attended to one of the victims, Perivolaris started moving down the street.

“(I) just started checking vitals on the first victim that I found. Vitals were absent and I started moving down the street, just checking on bodies. By the time I got to the fifth body, I had realized this was a massive casualty (event) that had occurred.”

Perivolaris would later learn that 10 people were killed and 16 others were injured in the deadly van attack.

At 1:26 p.m., John Shirley, an advanced emergency medical dispatcher and 14-year-veteran with Toronto EMS, answered one of the first 911 calls to come through on that day.

“Our caller was quite calm. He was able to describe everything that was happening on scene,” Shirley said.

“Towards the end of the call he had said something which made me think there is more to this than your typical pedestrian struck,” Shirley said. “The way he just described it. There was a lot more to the story than this.”

Shirley told CTV News Toronto that, at the time, everyone’s light in the communications centre was red, indicated they were on a 911 call.

“You can hear other call takers describing similar events to what our caller had said.”

But according to Shirley, the location for the incident was changing.

“It wasn’t just one intersection, it was a few more,” he said. “It took me a few minutes to figure out that we had multiple patients.”

Shirley said that 26 Toronto EMS vehicles were dispatched to the scene, including ambulances and a multi-patient bus. About 46 paramedics and command staff were involved in managing the incident.

One of the paramedics was Christopher Rotolo, who was offloading a patient at Mount Sinai Hospital when he heard the first radio communications about the attack. He was dispatched to Yonge Street and Park Home Avenue, where he was handed a patient in critical condition.

“We just loaded up the patient on our stretcher and transported to Sunnybrook Hospital as quick as we could,” Rotolo said.

He describes the scene as “surreal.”

“It was like nothing I’ve ever seen before,” he said. “People still needed to be triaged and people lying on the ground and a lot of the panic with all the bystanders on scene, and you know crews still responding from every angle. It was surreal. It was like nothing I’ve ever seen before.”

Rotolo said that he didn’t get a sense of the scale of the attack until he got home and turned on the news.

“I know I responded to it, but when I got home and actually turned on the news and started watching .. all the newsfeeds of what happened and seeing the aerial shots and seeing all the other emergency responders responding, I never got a true sense until I actually sat down and watch the news,” he said.

That sentiment was echoed by many of the first responders who attended the scene that afternoon.

“You can only go with what the information you're hearing on the phone, what callers on scene are describing. You can kind of paint your own image in your head as to what this looks like. When you start seeing it on the news, it changes things a little bit,” Shirley said.

“I didn’t know that there was that many more until after I got back dealing with the situation. And then I realized it was more than five, it was closer to 10 or so,” Perivolaris said. “I was driving home and that’s when it really impacted me and I actually got very angry for the, just the chaos that occurred here for no reason. These are innocent people going about their daily chores and their work and their families and they are gone because of a selfish act. It really, it got me very angry.”

But Perivolaris said that on the one-year anniversary of the deadly incident, he isn’t focusing on his anger or the tragedy that he witnessed. Instead, he is focusing on the community that supported the first responders who attended the scene.

“It was pretty amazing, from my perspective, as to how we all worked together. Not even just emergency services and special constables, but you know pedestrians, shop owners, anybody and everybody that was driving by or walking by kind of ran towards the incident and the scene instead of what you would expect is people to be fleeing from the area.”

“It’s a beautiful community here and the residents and the people that are around here, they were a great support that day and I won’t forget that they pulled together for us.”

With files from CTV News Toronto's Scott Lightfoot