It is not known if the suspect has been arrested, but WCVB reporter Kristen Setera tweeted that "an arrest is imminent or may have already taken place."
Law enforcement obtained video surveillance from a Lord and Taylor department store and a local television station that shows a man placing a black bag into the garbage can where the second bomb was set.
John King, of CNN, said the footage is believed to give a "clear identification, including a facial image of a suspect."
Though the details about the man have not been released, it has been reported that he is a dark-skinned male.
In the video, the man sets down a black bag thought to be containing a bomb just before the second was set off before 3 p.m. on Monday.
Boston Mayor Thomas M. Menino confirmed that a suspect was identified and officials are going to speak to the press at 5 p.m. Wednesday. The Boston Globe said that officials might make their findings public at the briefing.