FBI Agent Richard DesLauriers says the images came from surveillance cameras near the explosion sites shortly before the blasts.
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"We consider them to be armed and extremely dangerous," DesLauriers said, asking the public not to approach the men.
Monday's blasts killed three and injured more than 180.
The images were released hours after President Barack Obama attended an interfaith in Boston to remember the victims, including an 8-year-old boy.
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