Feds Race to Trace Boston Marathon Pressure Cooker Bomb

April 17, 2013 — -- Bombers who killed three people at the Boston Marathon Monday used a pressure cooker pot that's widely available for as little as $140 from major retail stores to house at least one of the explosives, officials told ABC News.

Investigators said Tuesday they had recovered a mangled Fagor brand pressure cooker pot, shrapnel, a circuit board and wiring from what they said was a partially exploded device near the finish line. The evidence has been sent to FBI's lab in Quantico, Virginia, where law enforcement sources said the parts could provide a break in the case.

Investigators will use every clue, from the pressure cooker's manufacturer and retailers to the types of nails used in the shrapnel, to try and find out from where the bomb parts were purchased and by whom, the sources said.

COMPLETE COVERAGE: Terror at the Boston Marathon

Richard Clarke, former White House counter-terrorism advisor and now ABC News consultant, said that while pressure cooker IEDs have been found in Afghanistan and Pakistan, that doesn't necessarily point to foreign involvement, as the pots are so widely available and instructions for how to build the bombs are easily accessed online by anyone.

"It doesn't tell you much about who did it... But it does give you a lead perhaps of where it came from," Clarke said. "They [investigators] may be able to trace back a pressure cooker."

Two bombs exploded Monday, but investigators said there was not enough evidence to determine if the second bomb was also built from a pressure cooker.

Along with tracking down the origin of the bomb parts, authorities are painstakingly going through hundreds of pictures and videos from the site of the bombing, hoping, as Clarke put it, to "stitch" together a picture of what exactly happened.

Adding to the pile of potential evidence in this case, a local news station, WHDH, has come forward to give investigators footage that shows a large sack in front of a metal fence just seconds before one of the bomb detonates, after which the large bag had disappeared. Then there's a series of still images taken by witness Ben Thorndike from a nearby office building. In those, Thorndike said he can see one man with tattered, seemingly burned clothes, sprinting from the scene immediately after a blast.

CLICK HERE to see the images from the site.

Authorities have not said that man -- or any other individual -- is a suspect in the case, but they have repeatedly urged any witnesses to come forward with any potential piece of evidence. They are currently looking for any information on someone who was carrying an unusually heavy dark backpack in the area before the race. The FBI requests anyone with potential information call 1-800-CALL-FBI.

"Assistance from the public remains critical in establishing a timeline of events which leads to swift conclusions through due diligence and strong investigative activity," FBI special agent in charge Richard DesLauriers said Tuesday. DesLauriers said then investigators have received "voluminous" tips and brought in additional evidence response teams to help deal with the massive workload.

READ ANALYSIS: How Feds Will Investigate Boston Marathon Bombing

At approximately 2:50 p.m. EST Monday, twin explosions went off near the finish line of the Boston Marathon, killing three people and injuring more than 170 more, more than a dozen critically. No group, domestic or international, has claimed responsibility.

Despite more than 36 hours passing without a suspect named, Clarke said he's confident the authorities will get their man.

"It may take a while, but this will be solved," he said.

Have a tip related to this or another investigation? CLICK HERE to send it in.

ABC News' Randy Kreider and Rym Momtaz contributed to this report.

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