Published April 17. 2013 9:00AM Updated April 17. 2013 6:19PM
BOSTON — Investigators poring over photos and video from the Boston Marathon bombing have a department-store surveillance-camera image of a man dropping off a bag at the scene of the one of the blasts, a top city politician said Wednesday.
City Council President Stephen Murphy, who said he was briefed by members of the Boston Police Department, said he does not know if investigators know the man's name. He said officers are chasing leads that could take them to the suspect.
"They may be on the verge of arresting someone and that's good," he said.
Separately, a law enforcement official who spoke to The Associated Press on condition of anonymity and was not authorized to discuss the case publicly confirmed only that investigators had an image of a potential suspect but did not know his identity.
The twin bomb blasts Monday near the finish line of the world's most famous foot race killed three people and wounded more than 170, tearing off limbs in a hail of shrapnel.
Law enforcement agencies pleaded for the public to come forward with photos, videos or any information that might help them solve the case, and they gathered surveillance video from businesses around the finish line.
The bombs are believed to have been fashioned out of ordinary kitchen pressure cookers packed with explosives, nails, ball bearings and metal shards designed to maim. Investigators suspect the bombs were hidden in black duffel bags and left on the ground.
As a result, they were looking for images of someone lugging a dark, heavy bag.
"One of the department stores down on Boylston Street submitted video system which has confirmed that a suspect is seen dropping a bag near the point of the second explosion and heading off," Murphy said.
Murphy said he was told investigators have matched information from the surveillance footage with witness descriptions of someone leaving the scene.
Earlier in the day, several news organizations, citing unidentified sources, reported that a video surveillance camera at a Lord & Taylor department store midway between the two blast sites showed a suspect with a backpack near the finish line.
The news came with Boston in a state of high excitement over conflicting information on whether a suspect was in custody.
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, 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.
"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."
The official who spoke to the AP about someone being taken into custody stood by the information even after it was disputed.
Scores of victims remained hospitalized, many with grievous injuries. Fourteen were listed in critical condition. Doctors who treated the wounded corroborated reports that the bombs were packed with shrapnel and blew up close to the ground.
The chief of trauma surgery at Boston Medical Center said most of the injuries his hospital treated were to the legs.
"We have a lot of lower-extremity injuries, so I think the damage was low to the ground and wasn't up," Dr. Peter Burke said. "The patients who do have head injuries were blown into things or were hit by fragments that went up."
The blasts killed 8-year-old Martin Richard of Boston and 29-year-old Krystle Campbell of Medford. The Shenyang Evening News, a state-run Chinese newspaper, identified the third victim as Lu Lingzi. She was a graduate student at Boston University.
A bomb threat forced the evacuation of the courthouse Wednesday midafternoon, the U.S. Marshals Service said, and security officials swept the area. Employees were allowed back in about an hour later.
Associated Press writers Jay Lindsay, Pat Eaton-Robb, Steve LeBlanc, Bridget Murphy, Rodrique Ngowi and Meghan Barr in Boston; Eileen Sullivan, Julie Pace and Lara Jakes in Washington; Paisley Dodds in London; Lee Keath in Cairo; and Marilynn Marchione in Milwaukee contributed to this report along with investigative researcher Randy Herschaft in New York.