Mark Boozell of Elmhurst was nearing the finish when the first of two bombs went off.
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"We saw the first responders headed that direction, so we stopped and started to jog the other direction and the second bomb went off," he recalled.
The bombing and ensuing manhunt for the bombers claimed five lives and injured some 300 more. At a solemn ceremony over the weekend, victims and first responders were among the attendees dedicating a commemorative finish line in Boston.
"We did not stop at the pain. We turned that pain into something that moves us forward and makes us better," said U.S. Senator Elizabeth Warren (D-Mass.).
The Boston bombing led to changes in security at large public events around the world, including the Chicago marathon, with increased police presences and less freedom of movement for fans and participants.
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"I think it's made all of us stronger, the city of Boston, made the Boston marathon stronger," said Carey Pinkowski of the Bank of America Chicago Marathon.
Boozell has run 16 marathons, but none like 2013 in Boston.
"It was surreal," he said. "It was an experience I'll never forget."
One of the two men believed to be responsible for the bombings was killed in a shootout with police. The other, Dzhokar Tsarnaev, remains in prison awaiting the death penalty.