Authorities said Tuesday that the two explosive devices that blew up near the Boston Marathon finish line were the only bombs found, and that there was no "imminent, physical threat" to the city.
Massachusetts Gov. Deval Patrick called the blasts an "act of terror."
Three people were killed in the explosions. Family members identified one of the victims as 8-year-old Martin Richard of Dorchester. Authorities have not released information about the other two fatalities.[embedgallery id=134983]
[videoembed id=134930]Boston Police Commissioner Ed Davis said a total of 176 people went to area hospitals. Of those, 17 were in critical condition Tuesday morning.
There was no advance warning, according to Davis, who said the marathon route was swept for explosives twice on Monday, with nothing found.
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No arrests have been made, but investigators were interviewing "a variety of witnesses at a variety of locations," according to FBI Special Agent in Charge Richard DesLauriers, who heads the Boston field office.
"This will be a worldwide investigation," DesLauriers said. "We will go to the ends of the earth to find the subject or subjects responsible for this despicable crime."
DesLauriers said authorities had received numerous tips from the public, but urged anyone with information — especially photos or video of the area — to send them to law enforcement.
"I would encourage you to bring forward anything. You might not think it’s significant, but it might have some value to this investigation,” Massachusetts State Police Superintendent Colonel Timothy Alben said.
Witnesses were asked to call the FBI hotline, 800-CALL-FBI, and press option 3. Photos and videos should be emailed to firstname.lastname@example.org or email@example.com.
At midday Tuesday, 12 blocks remained closed off as a crime scene, which Davis called "the most complex crime scene in the history of the department."
Investigators were working to open the area, but full access could be limited for several days, Davis said, asking people to be patient.
"We want people to come and go. We want you to live your life," Davis said, adding, “We want you to be vigilant. ... Give us a little room in the Copley Square area.”
Boston Mayor Thomas Menino, himself released from the hospital only Monday, urged residents to be compassionate and cooperative.
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