Top administration officials have arrived at the White House to discuss the Boston Marathon bombings with President Obama.
Rick DesLauriers, the special agent in charge of the FBI's Boston division, told reporters Tuesday that there was "no known imminent physical threat at any location where we might be conducting investigation right now."
Officials also announced a twist in the probe: Suspicious packages that were detonated out of precaution were not explosive devices after all.
Massachusetts Gov. Deval Patrick announced Tuesday that there were only two bombs -- the two that exploded at the marathon, killing three people and wounding 176.
A doctor who treated some of the wounded said Tuesday the wounds were caused by shrapnel that included pellets and nails. Seventeen of the injured remain in critical condition.
Authorities including bomb experts searched an apartment in Revere, Massachusetts, and removed items late Monday. But officials cautioned that there are currently no clear suspects -- and the motive remains unknown.
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