Several media outlets reported that a suspect had been identified from surveillance video taken at a Lord & Taylor department store between the sites of the bomb blasts.
The turn of events came with Boston in a state of high excitement over conflicting reports of a breakthrough.
A law enforcement official briefed on the investigation told the AP around midday that a suspect was in custody. The official, who was not authorized to divulge details of the investigation and spoke on the condition of anonymity, said the suspect was expected in federal court. But the FBI and the U.S. attorney's office in Boston said no arrests had been made.
By nightfall, there was no evidence anyone was in custody. No one was taken to court. The law enforcement official, who had affirmed there was a suspect in custody even after federal officials denied it, was unable to obtain any further information or explanation.
At least 14 bombing victims remained in critical condition. Dozens have been released from hospitals, and officials at three hospitals that treated some of the most seriously injured said they expected all their remaining patients to survive.
On Wednesday, investigators in white jumpsuits fanned out across the streets, rooftops and awnings around the blast site in search of clues. They picked through trash cans, plastic cup sleeves and discarded sports drink dispensers.
Boston remained under a heavy security presence, and some people admitted they were nervous about moving about in public spaces.
Tyler King, a personal trainer from Attleboro who works in Boston, said four of five clients canceled on him a day earlier because they were worried about venturing into the city. He took the train in, but "I kind of kept my head on a swivel."
Kenya Nadry, a website designer, took her 5-year-old nephew to a playground.