President Barack Obama on Monday said that the person or group responsible for the two explosions that wracked the 117th running of the Boston Marathon, will be brought to justice.
The latest casualty counts are two dead - including an eight-year-old child, according to reports - and more than 140 wounded after the explosives went off shortly before 3 p.m. near the finish line for the race.
Obama cautioned that the situation remains fluid, and that investigators do not have enough facts - but he was crystal clear on the consequences.
"We still do not know who did this or why," Obama told the nation. "And people shouldn't jump to conclusions before we have all the facts. But make no mistake -- we will get to the bottom of this. And we will find out who did this; we'll find out why they did this. Any responsible individuals, any responsible groups will feel the full weight of justice."
Obama stopped short of calling it a terrorist act, although the FBI is treating it as such - although it remains unclear if it a foreign or domestic act.
No one has claimed responsibility for the act.
Demolitions experts have reportedly located and disarmed a third device.
Police have questioned a number of people of interest throughout the day, but there have been no arrests and no suspects.
"I've updated leaders of Congress in both parties, and we reaffirmed that on days like this there are no Republicans or Democrats - we are Americans, united in concern for our fellow citizens," Obama said.
People have been told to remain where they are, and cell phone service in the city has been shut down in case it could possibly be used to trigger any further explosions.
Officials are also painstakingly sweeping the city for any other suspicious objects following a race that had attracted more than 27,000 runners.
Logan International Airport remains open, although all flights are being thoroughly checked.
There have been heightened security measures put into place in Washington D.C. and New York City.
There was no prior warning of any kind, officials have said.
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