As more details emerge of the Boston Marathon attack, authorities have said an eight year old boy, Martin Richard, was killed in the blasts. His mother and sister were also seriously injured.
The bombs exploded 4 hours into the marathon, turning the carnival atmosphere into one of terror. Bostonians had turned out on their public holiday to mark Patriots Day, which remembers the first battles of the American War of Independence.
Spectators were cheering as runners finished the race. The final mile had been dedicated to the victims of the Sandy Hooke Elementary School shooting, and some of the families were sitting near the finish line.
There are early reports coming out of Fox News that the FBI are searching an apartment in a suburb of Boston, with speculation that those responsible could have links to the Pakistani Taliban.