A twin bomb attack killed at least three – an eight-year-old boy among them – and injured at least 130 others near the finish line of the Boston Marathon, raising the spectre of renewed terrorist attacks on U.S. soil.
The carnage was loaded with horrible symbolism, striking the heart of downtown Boston during its marquee event on a state holiday commemorating the opening battles of the American Revolution.
In video footage of the initial blast, a race clock marks the tragic moment down to the second – 4:09:44 – timed a few minutes before the average finishing time of last year's race.
During the ensuing seconds, some exhausted racers duck, fall and turn away from the north side of Boylston Street, where an orange flash is followed by a white plume of smoke. Amid the screams, broken glass, bloodied pavement and fleeing runners, a second blast can be heard fewer than 100 metres down the course.
The resonance of those images with recent history was hard to ignore: tides of people surging down the streets of a major U.S. city away from fire and smoke.
"We still do not know who did this or why, and people shouldn't jump to conclusions before we have all the facts," President Barack Obama said in a televised statement. "But make no mistake, we will get to the bottom of this. And we will find out who did this."
By the time night had fallen, the site of the bombing was cordoned off and the surrounding streets bristled with law-enforcement vehicles and personnel. There were strange, sudden sirens – an ambulance, a racing fire truck – but also unexpected kindness. A woman in a windbreaker walking a dog spotted a group of runners and asked, "Are you all set for housing and such?"
The explosions erupted along the Boston Marathon's 26th and final mile, dedicated during a pre-race ceremony to the 26 lives lost in the Newtown school massacre. Families of the children and teachers murdered in Sandy Hook Elementary school were reportedly sitting in a VIP area near the finish line when a fireball flashed at 2:50 p.m., mere metres from where weary runners were raising their fists in triumph.
President Obama did not evoke 9/11 or make any mention of terrorism in his remarks, but White House officials told reporters they are indeed treating the attack as "acts of terror."
Witness reports from the scene after the bombings stood in grave contrast to the elation that marked the race just moments before.
"They just started bringing people in with no limbs," said runner Tim Davey, of Richmond, Va.. He said he and his wife, Lisa, tried to keep their children's eyes shielded from the gruesome scene inside a medical tent that had been set up to care for fatigued runners, but "they saw a lot."
"They just kept filling up with more and more casualties," Ms. Davey said. "Most everybody was conscious. They were very dazed."
Organizers initially diverted runners before cancelling the marathon altogether, stranding several thousand runners on the course and touching off a chaotic evacuation effort. Buses whisked away hundreds of weary participants, others began suffering symptoms of hypothermia as they waited on the race route for upward of an hour following the blasts.
Cellphone towers were reportedly shut down citywide to prevent remote detonations and flights out of Logan Airport were grounded until 5:30 p.m.
Within hours of the twin explosions, law-enforcement agencies were dealing with dozens of reports of suspicious packages across the city, stretching bomb squads and canine units.
There was no word on the motive or who may have carried out the attack, and police said they had no suspects in custody and no threats in advance. According to news reports, a senior U.S. intelligence official said two other explosive devices were found near the end of the 26.2-mile course.
The 2013 race drew more than 23,000 participants, including 2,078 Canadians.
"We were just waiting for dad when directly centre from us and across the street there was this loud, loud bang," said Stefan Graci, who travelled from Toronto to Boston to watch his sister and father run. Their seats, he said, were so close they "could see people lying motionless."
Mr. Graci said some were injured, while others stood stunned.
He said the first explosion was mainly sound, but the second seemed bigger with a bigger plume of smoke and shockwaves carrying over into the street.
"That's when people realized what was happening and we decided to get the hell out of there."
The Boston Marathon is considered one of the world's premier athletic events. Founded in 1897, it is the world's oldest annual marathon and often attracts more than 500,000 spectators. Manulife Financial Corp.'s U.S. subsidiary, John Hancock Financial Services Inc., has been lead sponsor for the past 28 years, including the 2013 race. A spokesman for Manulife said the company would not comment at this point and was waiting for the authorities to release more information.
An official from the Department of Foreign Affairs said that as of 9 p.m. there were no reports of any Canadians affected by the blasts.
Organizers of the London Marathon, the next major event on the international marathon calendar, are reviewing security plans for the event.
"Our security plan is developed jointly with the Metropolitan Police and we were in contact with them as soon as we heard the news," said Nick Bitel, London Marathon chief executive.
"We are deeply saddened and shocked by the news from Boston. Our immediate thoughts are with the people there and their families. It is a very sad day for athletics and for our friends and colleagues in marathon running."
Boston's social calendar crept to a halt as the day wore on, with the NHL's Bruins cancelling a home game against the Ottawa Senators and the Symphony calling off its Monday performance. Mr. Obama chose to focus on the city's resolve.
"Boston is a tough and resilient town," he said. "So are its people. I'm supremely confident that Bostonians will pull together, take care of each other and move forward as one proud city. And as they do, the American people will be with them every single step of the way."
Canadians in Boston in need of assistance can contact the Consulate General at (617) 247-5100.
If you're a Canadian who was at the marathon, The Globe would like to hear from you. E-mail email@example.com