Investigators believe they have spotted a suspect in the Boston Marathon bombing from security video, a U.S. law enforcement source said on Wednesday, but no arrest had yet been made.
Police may make an appeal to the public for more information at a news conference scheduled for later on Wednesday, a U.S. government source said.
Earlier, cable news network CNN reported a suspect was in custody, citing Boston and U.S. law enforcement sources, but it later retracted its report.
Three Reuters sources also disputed there had been an arrest. Officials later confirmed the arrest report was inaccurate.
The suspect in the video had not yet been identified by name, two U.S. government officials said.
"Despite reports to the contrary there has not been an arrest in the marathon attack," Boston police said in a statement.
The U.S. Federal Bureau of Investigation (FBI) issued a statement asking the media to "exercise caution and attempt to verify information through appropriate official channels before reporting."
Shortly after the false arrest report, security officials at Boston's federal courthouse ordered staff, media and attorneys to evacuate and move at least 100 yards (91.4 meters) away, according to a Reuters reporter on the scene.
Bomb-sniffing dogs and fire engines arrived at the courthouse.
The identification of a possible suspect marked the most significant, publicly-disclosed break since Monday's blasts at the Boston Marathon's finish line killed three people and injured 176 others in the worst attack on U.S. soil since Sept. 11, 2001.
The bombs killed an 8-year old boy, Martin Richard; a 29-year-old woman, Krystle Campbell, and a Boston University graduate student who was a Chinese citizen. Boston University has identified the student as Lu Lingzi.
The crowded scene in central Boston was recorded by surveillance cameras and media outlets, providing investigators with significant video of the area before and after the two blasts.
Investigators were also searching through thousands of pieces of evidence from cellphone pictures to shrapnel pulled from victims' legs.
Based on the shards of metal, fabric, wires and a battery recovered at the scene, the focus turned to whoever may have placed homemade bombs in pressure cooker pots and taken them in heavy black nylon bags to the finish line of the world-famous race watched by thousands of spectators.
Streets around the bombing site remained closed to traffic and pedestrians on Wednesday, with police continuing their work.
SENSE OF RELIEF
Rich Havens, the finish area coordinator at the Boston Marathon who also witnessed Monday's blasts, said he was relieved officials had identified a suspect.
"When the police said we are turning every rock, they really meant it," Havens said. "There is a sense of relief that the amazing work they are doing - breaking through bits and pieces - is actually turning things up. And that they've gotten to this point in a matter of two days."
Bomb scene pictures produced by the Boston Joint Terrorism Task Force and released on Tuesday show the remains of an explosive device including twisted pieces of a metal container, wires, a battery and what appears to be a small circuit board.
One picture shows a few inches of charred wire attached to a small box, and another depicts a half-inch (1.3 cm) nail and a zipper head stained with blood. Another shows a Tenergy-brand battery attached to black and red wires through a broken plastic cap. Several photos show a twisted metal lid with bolts.
No one has claimed responsibility for the attack.
"Whether it's homegrown or foreign, we just don't know yet. And so I'm not going to contribute to any speculation on that," said U.S. Secretary of State John Kerry, who until January was Massachusetts' senior senator. "It's just hard to believe that a Patriots' Day holiday, which is normally such time of festivities, turned into bloody mayhem."
The head of trauma surgery at Boston Medical Center, which was still treating 19 victims on Wednesday, said his hospital was collecting the shards of metal, plastic, wood and concrete they had pulled from the injured to save for law enforcement inspectors. Other hospitals were doing the same.
"We've taken on large quantities of pieces," Dr. Peter Burke of Boston Medical Center told reporters "We send them to the pathologists and they are available to the police."
Security officials who spoke on condition of anonymity said instructions for building pressure-cooker bombs similar to the ones used in Boston can be found on the Internet and are relatively primitive.
Pressure cookers had also been discovered in numerous foiled attack plots in both the United States and overseas in recent years, including the failed bombing attempt in New York's Times Square on May 1, 2010, the officials said.
Additional reporting by Mark Hosenball in Washington and Scott Malone in Boston; editing by Daniel Trotta and Gary Crosse