A law enforcement official briefed on the investigation told The Associated Press earlier in the day that a suspect was in custody. The FBI and the U.S. attorney's office in Boston said that no arrests had been made.
The official who spoke to the AP did so on condition of anonymity and stood by the information even after it was disputed. The official, who was not authorized to divulge details of the investigation, had said the suspect was expected in federal court in Boston.
Reporters and police converged at the courthouse.
Several media outlets reported that a suspect had been identified from surveillance video taken at a Lord & Taylor store between the sites of the two bomb blasts, which killed three people and wounded more than 170.
A news briefing was scheduled later Wednesday.
"Contrary to widespread reporting, there have been no arrests made in connection with the Boston Marathon attack," the FBI said in a statement. "Over the past day and a half, there have been a number of press reports based on information from unofficial sources that has been inaccurate. Since these stories often have unintended consequences, we ask the media, particularly at this early stage of the investigation, to exercise caution and attempt to verify information through appropriate official channels before reporting."