Jean-Paul Bedard clearly remembers the ear-piercing blasts, the ominous plumes of smoke and the total pandemonium that erupted moments after two bombs went off at last year's Boston Marathon.
The enormity of the situation only hit home days later though, when the 47-year-old was back in Toronto looking at a video his wife had taken of him crossing the finish line -- there, in a short clip, appeared to be one of the backpacks authorities believe contained explosives which ripped through the crowd.
"She was just standing there in harm's way that whole time," he said of the footage the couple later sent to the FBI. "I was a bit late, an hour later than I normally am and if I had been an extra 20 minutes, she would have been right there."
The realization triggered an avalanche of emotions and Bedard, an avid runner, initially vowed never to return to the Boston Marathon again.
Yet, like many other Canadians, the English teacher is now heading back to the city and plans to run the course again next week. Bedard, however, plans to run the marathon not once, but twice in the same day.
"I needed to go back there," Bedard said, adding he had secured permission from race authorities to run a double marathon.
The twin blasts which killed three people and injured more than 260 others on April 15 last year came to symbolize a turning point in Bedard's life.
Just weeks before last year's race, Bedard told his family about sexual abuse he suffered as a child. During the marathon, he had a breakdown and was stopped by medics but managed to convince them he was hurting mentally, not physically, and carried on.
He finished the race, returned to his hotel room for a quick shower and was back outside with his wife, 100 metres away from the finish line on a parallel street when the bombs went off.
When he returned home, the combined stress of his personal issues and the bombings led to Bedard being diagnosed with post traumatic stress disorder. After a year of treatment, he's returning to confront the trauma and move past it.
"I feel a lot of weight on my shoulders in doing this," he said. "But at the same time I feel like I'm being carried by a lot of people to get through this."
Bedard is among a number of Canadians who were at the marathon last year and felt the urge to participate once more.
"It's something that I need to do and I want to do," said Dean Simon, a Newfoundland native who was one kilometre away from the finish line when he was stopped by race officials last year.
The 46-year-old recalls trying to calm some of the panicked runners around him as word of the explosions spread. The worst part for Simon was not being able to call his mother for hours, to let her know he was safe.
Simon only realized much later that a fall earlier that day, which had slowed him down considerably, likely saved him from being among the victims.
"I could have very easily been at that line," he said, his voice shaking. "It really isn't sinking in until now."
The blasts also made Linda Hensman realize how fortunate she was.
"Every so often you need something to bring life back into perspective. To slow you down, to make you appreciate what you have," said the 62-year-old who was also stopped before she could finish the race last year.
"I just wanted to go back under what I hope will be normal circumstances...I don't think you can let these events hijack your life."
Race officials say 2,447 people from Canada have registered to take part in this year's marathon, up from 2,032 registered last year.
Four days after last year's blasts, police killed one of the suspected bombers, 26-year-old Tamerlan Tsarnaev, in a shootout and captured his brother Dzhokhar Tsarnaev, who was 19 at the time, soon after.
Prosecutors say the Tsarnaev brothers built two pressure cooker bombs and planted them near the race's finish line.
The brothers had lived in the former Soviet republic of Kyrgyzstan and the Dagestan region of Russia before moving to the U.S. with their family about a decade before the bombings.
