Boston Marathon bombing victim Patrick Downes (left), who lost a leg in the bombing, crosses the finish line of the 2017 Boston Marathon with Adam Keys in Boston, Massachusetts, US, April 17, 2017. [Photo/Agencies]

Meb Keflezighi, who in 2014 became the first American to win the race in over three decades, finished 13th in his final Boston Marathon.

Keflezighi, who plans to retire from racing after the New York City marathon in November, stopped after his victory to touch the hand of Bill Richard, whose 8-year-old son Martin was the youngest person to die in the bombing.

"In 2013, I was a spectator just like the three victims and when I saw the 8-year-old ... the first thing in my mind was that could have been my daughter," said Keflezighi.

Tens of thousands of people packed the streets for Boston's largest sporting event, held on the Patriots Day holiday, which commemorates the start of the American Revolution.

Reuters