The heart of Boston has turned into a crime scene.
On a cold, pale weekday morning, officers in uniform and military police in fatigues manned barricades at all the streets leading to the area near the bombings.
Along the marathon route, nothing appeared to have been touched – not the flags, not the sponsor signs, not the folding chairs used by spectators, not the usual race detritus of water bottles and banners.
A trio of local Boston police officers stood near a barrier in the morning cold, stamping their feet to keep warm after spending the entire night on watch.
"We have to keep the integrity of the scene," one of them said. "There are so many pieces still there, so many pieces still to look for."
On Newbury Street, a restaurant's outdoor patio served as testament to the fact that life can change in an instant. Many chairs were draped with the blankets used to warm marathoners after the race. But on the tables were half-finished meals – a burger, a plate of fried calamari – abandoned in haste.
Federal investigators said no one had claimed responsibility for the bombings, which killed three people including an eight-year-old boy. But the blasts among the throngs of spectators raised fears of a terrorist attack.
President Barack Obama was careful not to use the words "terror" or "terrorism" as he spoke at the White House on Monday after the deadly bombings, but an administration official said the bombings were being treated as an act of terrorism.
"We will find out who did this. We'll find out why they did this," the President said. "Any responsible individuals, any responsible groups, will feel the full weight of justice."
As many as two unexploded bombs were found near the end of the 26.2-mile course as part of what appeared to be a well-co-ordinated attack, but they were safely disarmed, according to a senior U.S. intelligence official, who also spoke on condition of anonymity because of the continuing investigation.
The FBI took charge of the investigation into the bombings, serving a warrant late Monday on a home in suburban Boston and appealing for any video, audio and still images taken by marathon spectators.
Bostonians began to find their way to work on a morning unlike any other, while marathon runners started to return home.
Richard Snyder, a runner from Maryland, gazed toward the blocked-off route and sighed when asked whether he would compete in Boston again. "I would come back, but I don't know if I'd put my wife through that – the worry," he said.
He has run marathons since the 1980s, including numerous times in Boston. He and his wife were planning to find the soonest flight home they could afford, cutting short their usual post-race celebration: a walk around town, a nice dinner.
Cecilia Velasco hurried toward her morning train along abnormally hushed streets. She said she had just seen an armoured jeep outside her house. "I was a little scared," said the 31-year old. "I thought everyone was gone."
With a report from The Associated Press
Canadians in Boston in need of assistance can contact the Consulate General at (617) 247-5100.