BOSTON — Federal investigators reported Wednesday they have viewed video of a possible suspect in the Boston Marathon bombings that shows the person totting a heavy black bag into the finish line area and perhaps dropping it there.
They said they were close to identifying the individual but firmly denied media reports that they had made an arrest. The video apparently shows the bag at the site of the explosion that occurred 12 seconds after the first bomb went off. Three people were killed and 176 injured.
Based on remnants of the bombs at the crime scene, officials said the explosives appeared to have been hidden in black duffel bags or backpacks, and left about 100 yards apart in the areas cordoned off for spectators.
They said the bombs were comprised of nails, ball bearings and other small metal objects sealed in common kitchen pressure cookers that were either timed to explode or remotely detonated. Once they discharged, the encased projectiles sprayed scores of people, causing death, loss of limbs and many other major injuries.
A spokesman for Boston Mayor Thomas M. Menino said that a surveillance camera at the Lord & Taylor department store across from the second bomb site was the "best source of video so far" in identifying who perpertrated the carnage. But officials would not say if that was the video that contained the image of the possible bag-carrying suspect.
Investigators have pored, frame-by-frame, through hundreds of photos and video taken by security cameras, television stations and spectators since the bombings Monday afternoon that President Obama called an "act of terrorism."
Obama will attend a special interfaith prayer service for the victims at 11 a.m. Thursday at Boston's Cathedral of the Holy Cross. It will be the fourth time in the past several months he has been present for such an event, the most recent being the Newtown, Conn., school massacre.
Mid-day reports by CNN, AP and local media outlets that a suspect had been taken into custody and would be arraigned at the federal courthouse caused confusion across the city. Hordes of reporters quickly gathered at the waterfront courthouse in anticipation of the suspect's appearance only to be told no one had been arrested.
In the two days since the bombings, forensic experts wearing white coveralls and getting down on their knees have meticuously checked the crime scene for bomb scraps and blood stains for any possible DNA evidence tied to known terrorists.
Officials Wednesday identified the third person killed in the bombings as Lingzi Lu, 23, a Chinese graduate student studying math and statistics at Boston University. Friends said she had gone to the marathon with two other Chinese students, one of whom was seriously injured. Lu, an only child, grew up in Shenyang in northeast China. Her father was en route to Boston to claim his daughter's body.
The bomb blasts also killed 8-year-old Martin Richard of Boston, who was at the marathon with his family, and 29-year-old Krystle Campbell, a restaurant manager from Arlington, Mass., who had gone to the race to take a photo of her girlfriend's boyfriend crossing the finish line.
Several of the injured remained in critical condition at Boston hospitals, suffering shattered bones and severe shrapnel wounds. At least eight of the wounded underwent leg or arm amputation operations.
Dr. Peter Burke, chief of trauma surgery at Boston Medical Center, said many of the victims arrived in the emergency room with metal objects deeply embedded in their flesh and with destroyed blood vessels, and with shredded muscle and fat.
"As an orthopedic surgeon, we see patients like this, with mangled extremities, but we don't see 16 of them at the same time, and we don't see patients from blast injuries," said Burke.
Richard DesLauriers, the Boston FBI agent in charge of the investigation, said evidence collected so far at the scene includes parts of a pressure cooker, a circuit breaker, a battery with wires attached, and countless pieces of metal such as nails, ball bearings and buckshot-like BBs. Hospital doctors also turned over the pieces of shrapnel removed from the victims' bodies.
DesLauriers said the forensic evidence is being sent to the FBI laboratory in Quantico, Va., for analysis and to reconstruct the bombs and try to find out where the material in them might have originated. Pressure cooker explosives were found in the bomb attempt in New York's Times Square in 2010, and they have been used by terrorists in India, Nepal, Pakistan and Afghanistan.
The FBI agent urged anyone who was present at the crime scene at the time of the explosions and may have seen anyone carrying a heavy black duffel bag or backpack to contact authorities. He also asked for tips on anyone who may have talked about a bombing before the marathon.
"The person who did this was someone's friend, co-worker or neighbor," said DesLauriers. "Somebody knows who did this."
Details for this story were provided by law enforcement officials.