Gary Allen of Cranberry Island said he ran faster than he probably should have given his injured leg and level of fitness in the Boston Marathon April 15, accounting for when he crossed the finish line.

About half hour later, the first of the two explosions detonated about 150 yards from the media center he had walked to at Fairmont Copley Plaza.

“It was big,” he said. “A loud audible boom.”

He said the explosion shook the building and he now realizes he could have been there when it took place.

“A lot of people were there,” he said, adding that the images of those injured were “heartbreaking.”

He said he would gladly give back the medal he received for finishing if everyone could be OK.

He said the coverage of the event has switched from celebratory to a very somber day.

“People are in shock. It's very sad,” he said.

He said the second explosion came about 10 seconds after the first, leading him to believe this was a coordinated attack of some sort, though he said he did not know whether it was by domestic or foreign forces. A water cannon was used later, which he said is sometimes a way of dealing with a suspicious device, so there was concern of more danger.

The runners in the race who had not finished were detoured off the route to hopefully be reunited with their families. Allen said the building he was in has been “locked down” with no one allowed to enter or leave.

“This is a big day for tens of thousands of people,” he said. Allen, who founded the MDI Marathon said this was his 21st Boston Marathon. He said the event is one of the greatest American traditions, going back 117 years.

He said he wonders now how events like this can be held that attract large crowds that some might want to hurt.

As for Allen, he said he is sure the full weight of this has not yet struck him.

“I'm exhausted,” he said. “I just poured myself into this marathon.” He said he is still covered in salt from the sweat of the event and now he is emotionally “wrecked” by what has happened.

“It's going to be a hard thing,” he said, dealing with this.