Two explosions around 2 p.m. at the finish line of the Boston Marathon resulted in at least three deaths.
The explosions Monday also injured more than 130 people, knocking spectators and at least one runner off their feet.
Some of the victims lost arms and legs. Other injuries included broken bones, shrapnel wounds and ruptured eardrums.
Spectators and runners described the twin explosions.
One woman says she was waiting for her husband to cross the finish line, and, in her words, "it just blew." She described it as "a loud boom, and then glass everywhere." Cherie Falgoust says something hit her head, and she "just ducked."
A runner, Laura McLean of Toronto, says she heard two explosions outside the medical tent. She says, "There are people who are really, really bloody." McLean says, "they were pulling them into the medical tent."
The explosions took place about three hours after the winners crossed the finish line. The second one could be heard a few seconds after the first one.
A runner said, "There are a lot of people down."
Marathon workers were seen carrying one woman, who did not appear to be a runner, to the medical area as blood gushed from her leg.