A bus carrying 25 New Brunswickers returned to Saint John from the Boston Marathon on Tuesday night as those runners were still reflecting on the tragedy that unfolded on Monday afternoon.

The United States has deployed more than 1,000 law enforcement officers to work on the investigation to find out who was responsible for the twin blasts that killed three people and injured more than 170 other people near the finish line of the marathon.

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Ellen Steeves described the pandemonium after the first explosion near the Boston Marathon's finish line. (CBC)

Garth Millar organized a bus trip to Boston and as the group members arrived back in Saint John on Tuesday night, they were still trying to process the horrific images they saw at one of the world’s most famous road races.

"The thing that sticks in my memory is watching people running towards me in tears. With their cell phones against their ears, trying to find out information and it’s almost like you're seeing it on television but its real," Millar said.

Millar said the day started out as expected. He watched 27,000 runners start the iconic Boston Marathon, an event many had been training months, if not years, to compete in.

"And four hours after that, we're dealing with death and mayhem, it's too hard to put into words," he said.

Ellen Steeves was watching racers complete the marathon on Monday and was about a kilometre from the first blast site.

She described the instant chaos that broke out when the bomb exploded.

"And then it instantly changed into pandemonium. The police started screaming, 'Stop the runners, stop the runners,'" she said.

"The police suddenly started racing towards the finish line."

Runners plan to return to Boston

Millar said the attacks will not stop him from organizing an annual trek to Boston.

For the last five years, he has organized the bus trip to the Boston Marathon and Millar said those future trips will still happen.

"It's not going to deter me from going back to Boston," he said.

"If I was lucky enough to qualify again for next year, I'd certainly go and run. I don't think we can stop doing things because of acts like this. If we do that, then the terrorists win."