At first, she felt shock. But then her training as a CPR instructor kicked in. The 34-year-old buckled her daughter in her stroller and yelled for her friend to watch her as she sprinted towards the victims.

She could see four.

Jefkins reached the first two and fumbled with the CPR mask on her key chain — shaking — before she abandoned her keys on the ground. She started chest compressions on one victim, a young woman, while calling out to the crowd for someone to help.

“But people were shell-shocked. They were staring. A lot of them were on their phones,” she remembers. “My clearest recollection is a woman literally screaming into her phone as she ran past me.”

A man approached and took over and she ran to the next victim, and the next. She did CPR until someone came to help, then circled back to check on the others.

“Push hard, push fast, you’re doing great, keep going, you’re making a difference,” she yelled at the bystanders who had come to help.

They were the same words she uses in her CPR classes. The same words she heard as a respiratory therapist and teenage lifeguard. But she’d never had to say them outside a hospital or training before. She would have appreciated someone saying them to her, she thought.

She remembers someone walking by and yelling that there were more victims up the street. But it was too far to run, and she already had enough to do where she was.

“We all kind of needed each other in that moment,” she says.

Soon emergency services arrived and took over. Later, she saw all four victims covered in orange tarps.

Walking home, Jefkins realized she’d left her keys and condo fob on the ground. They were now lost behind yellow tape, part of a vast crime scene.

Her husband met her and Eleanor at their building, so she could get inside. She took a long shower and left her bloodstained clothes at the door.

“The decompression comes later, which is the harder part,” she says. Those first few weeks were “low key,” taking care of her baby daughter helped her distract herself from second-guessing, ruminating on what she could, or should, have done differently.

That fall, she entered a graduate program at the University of Toronto to study the experience of being a bystander. It was always in the plan, even before the attack, to pursue an interest in the “myriad” feelings people say they wrestle with after witnessing a traumatic event.

“If there was any further confirmation from the universe that this is what I was supposed to do, that was kind of it,” she says. “This was my defining moment.”

Grad school has helped her to “unpack the experience.” To look at it through both a professional and personal lens. “But more importantly, also that I’m able to take this experience and share it with others, and share why it’s so important to become an active bystander.”

Her message, which she shared during a U of T Ted Talk in late March, is simple: “Do something.”

The first few moments are the most crucial, and it typically takes eight to ten minutes for paramedics to arrive. So bystanders make a difference. Getting trained in CPR is key, but even if you aren’t, trying is better than not, she says.

The bystander effect, where no one from a crowd steps up because they feel like someone else will, is well documented — she saw it that day.

But the bystander experience, what happens to them after they witness a trauma, what causes them to act or not act, and what support they need, is less studied. It needs to be, she says.