BOSTON - Authorities investigating the deadly bombings at the Boston Marathon have recovered a piece of circuit board that they believe was part of one of the explosive devices, and also found the lid of a pressure cooker that apparently was catapulted onto the roof of a nearby building.
The blasts near the finish line on Monday killed three people and wounded more than 170 people.
A law enforcement official briefed on the investigation confirmed to The Associated Press on Wednesday that authorities recovered what they believe are some of the pieces of the explosive devices. The official spoke on condition of anonymity because this person was not authorized to publicly discuss evidence in the ongoing investigation.
A person close to the investigation previously told AP the bombs consisted of explosives put in 1.6-gallon pressure cookers, one with shards of metal and ball bearings, the other with nails.
FBI special agent in charge Richard DesLauriers said Tuesday that pieces of black nylon and fragments of the metal shrapnel were found in the area. Because of the fabric, DesLauriers said investigators believe the bombs were placed in a dark-colored backpack or bag.
DesLauriers says whoever carried out the bombing at the marathon "is someone's friend, neighbor, co-worker or relative." That's why authorities are continuing to appeal to the public to report anything they may have seen or heard, even before the attack.
The law enforcement representatives have also asked for any video, audio and photos taken by marathon spectators, even images that people think might not be significant."There has to be hundreds, if not thousands, of photos and videos" that might help investigators, state police Col. Timothy Alben said.
Investigators have gathered a large number of surveillance tapes from businesses and intend to go through them frame by frame.
Officials say the theory is that someone knows who bombed the race.
The bomber may have been seen amid revelers, carrying an unusually heavy nylon bag, weighed down with shrapnel-packed explosives.
Similar pressure-cooker explosives have been used in Afghanistan, India, Nepal and Pakistan, according to a July 2010 intelligence report by the FBI and Homeland Security. Also, one of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker, the report said.
"Placed carefully, such devices provide little or no indication of an impending attack," the report said.
Federal investigators said no one had claimed responsibility for the bombings.
The Boston Marathon is one of the world's oldest and most prestigious races and about 23,000 runners participated. The attack may have been timed for maximum bloodshed: The four-hour mark is typically a crowded time near the finish line because of the slow-but-steady recreational runners completing the race and because of all the friends and relatives clustered around to cheer them on.
According to the race's website, 521 Colorado residents were registered to race Monday.