BOSTON — Two bombs exploded simultaneously near the finish line of the Boston Marathon Monday afternoon on Patriots Day, killing two spectators and injuring scores of other onlookers and runners.
Officers sweeping the area found another device in the vicinity, and detonated it. No other devices were found.
A fire-and-smoke incident less than two hours later at the cross-town John F. Kennedy Library was first thought to be related, but upon further investigation police determined it was an electrical fire and not connected.
The explosions near the finish line occurred more than four hours after the start of the race, and after 17,600 of the 27,000 runners had finished. The men's winner Lelisa Desisa of Ethiopia and the women's winner Rite Jeptoo of Kenya crossed the finish line two hours before the bombs went off.
Race organizers said most of the runners still completing the race at the time of the explosions were running for charity organizations and not among the elite marathoners.
The injured were first taken to medical tents set up to treat fatigued runners, then transferred by ambulance to Boston hospitals. Massachusetts General Hospital said six people taken there were in critical condition, five in serious condition.
Boston Police Commissioner Ed Davis said the marathon course bombs exploded at 2:50 p.m. in trash cans about 50 to 100 yards apart near the finish line on Boyleston street close to the Boston Public Library.
Witnesses reported a huge plume of white smoke, followed by a chaotic scene of screaming and crying by spectators lining the street and the runners approaching the end of their grueling 26.2-mile race.
Jill Harmacinski, a reporter covering the race for The Eagle-Tribune of North Andover, Mass., said the explosions sounded like gun shots. She said there was "blood all over Boylston Street" at and near the finish line.
"It was awful," said Harmacinski. "Everybody was running away from the smoke, and many of them were covered in blood. It was a confusing and scary scene."
President Obama phoned Gov. Duval Patrick and Mayor Thomas Menino after receiving a briefing from Homeland Security adviser Lisa Monaco on the situation.
"He offered the complete assistance of the FBI and all other federal agencies," the governor told a news conference. "Every resource at our disposal will be used to bring those responsible for this ghastly act to justice."
The president later addressed the nation from the White House press room, saying officials do not know yet who was behind the explosions or why.
"We still don't have all the facts," said the president. "We will get to the bottom of this. We will find who did this and we will find out why they duid this. any responsible individuals, any responsible groups, will feel the full weight of justice."
Obama noted that Monday was Patriots Day, a state holiday in Massachusetts commemorating the battles of Lexington and Concord and the start of the American Revolution more than 235 years ago.
"Boston is a tough and resilient town; so are its people," said Obama. "I'm sure the people of Boston will pull together."
Witnesses to the bombings said the explosions could be heard blocks away from the finish line area. Some said they sounded like cannon fire. Smoke from the bombs spread throughout the area, causing spectators and runners to choke and gag.
Runner Laura McLean of Toronto described a chaotic scene. "There are people who are really, really bloody," McLean said. "They were pulling them into the medical tent."
Cherie Falgoust, who was waiting at the finish line for her runner husband, said the explosions came from a nearby building, perhaps the Lenox Hotel.
"I don't know what this building is ... it just blew. Just a big bomb, a loud boom, and then glass everywhere," She said. "Something hit my head. I don't know what it was. I just ducked."
Almost 27,000 runners from 96 countries competed in the marathon, a signature event for Boston and the world running community. The elite runners, including the winners in both the men's and women's divisions, had finished the race two to three hours before the explosions.
Details for this story were provided by The Eagle-Tribune, North Andover, Mass., and witnesses.