The images released to the public were obtained by law enforcement from surveillance cameras in the city, FBI Agent Richard DesLauriers told reporters at a press conference to release the images.
The release follows Wednesday’s conflicting reports that a suspect had been identified, causing media confusion over whether any had been apprehended.
Earlier on Thursday, President Barack Obama and first lady Michelle Obama attended an interfaith service in memory of the dead.
The Monday attacks killed three people and wounded nearly 200.
Anyone with pertinent information should call 1-800-CALL-FBI, or 1-800-225-5324. DesLauriers said “We consider them armed and extremely dangerous.”