BOSTON (CBS) – Federal and local investigators are asking the public to come forward with information, photos, or video to help them track down who's responsible for the deadly explosions at the Boston Marathon finish line.
Officials said they had received 2,000 tips as of noon on Tuesday.
PHOTOS: Boston Marathon Bomb Evidence
Late Tuesday, the FBI released an intelligence bulletin that included a picture of a mangled pressure cooker and a torn black bag the FBI said were part of a bomb.
Three people were killed and 176 hurt when two bombs went off Monday afternoon on Boylston Street. 17 of the injured are in critical condition.
In a brief statement at the White House Tuesday, President Barack Obama said the FBI is now investigating it as an act of terrorism.
"We will pursue every effort to get to the bottom of what happened," the president told reporters before leaving without taking questions.
Obama is expected to come to Boston Thursday at 11 a.m. to attend an interfaith service at the Cathedral of the Holy Cross.
"We will go to the ends of the Earth to identify the subject or subjects who are responsible for this despicable crime, and we will do everything we can to bring them to justice," Special Agent-in-Charge of the FBI's Boston Field Office Richard DesLauriers said in a news conference Tuesday.
CBS News is reporting the two bombs were made to look like discarded property.
DesLauriers said in an evening press conference the bombs may have been in pressure cookers and were in dark-colored nylon bags or backpacks and would have been heavy to carry.
According DesLauriers, the bombs were laced with shrapnel ball bearings and nails.
The evidence has been sent to an FBI laboratory for testing.
"Someone knows who did this," he said.
DeLauriers urged business owners to go back over their surveillance video and for the public to remain alert.
Boston Police Commissioner Ed Davis said Copley Square is now "the most complex crime scene in the history of our department."
The commissioner told reporters the area around the crime scene has been reduced from 15 blocks to 12, but that it may take two more days to collect all the evidence there before it's completely re-opened to the public.
Davis said they are getting assistance from police departments in New York, Los Angeles, Chicago and Baltimore.
PHOTOS: Marathon Explosions
One of those killed was an 8-year-old boy, Martin Richard of Dorchester. His mother and sister were also injured in the blasts.
A second victim was identified Tuesday afternoon. Krystle Campbell, 29, of Medford, had gone with her best friend to take a picture of the friend's boyfriend crossing the finish line on Monday afternoon.
The third victim's name has not been released because next of kin has not yet been notified. Boston University has said the victim was a student at their school.
Investigators say no one has claimed responsibility and there's no word yet on a motive.
Authorities confirmed Tuesday that there were only two bombs and no other devices were recovered in Monday's search.
Davis said there were two security sweeps of the finish line area before the explosions - the first early Monday morning and the second just before the runners came in. Both searches turned up nothing, according to the commissioner.
Police and federal agents searched an apartment building on Ocean Avenue in nearby Revere late Monday night in connection with the bombings.
CBS News Senior Correspondent John Miller reported Tuesday morning the apartment search was related to a man who is reportedly under guard at Brigham and Women's Hospital.
They later reported the man was not a suspect in the bombing.
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Col. Timothy Alben, the superintendent of the Massachusetts State Police said people should expect to see an enhanced presence of police in the Boston area for the next few days.
"You will see troopers and the National Guard on the MBTA," he said. "We're doing that for the comfort of the public."
DesLauriers said there is "no known imminent, physical threat," but assistance from the public is critical.
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Patrick said there is a need for blood on a "sustained" basis at local hospitals. He urged members of the public to make appointments for next week and the following weeks to come.
Anyone who may have photos, video or information is asked to call investigators at 1-800-494-TIPS or 1-800-CALL-FBI.
You can also email them at firstname.lastname@example.org.
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