FBI: Boston Marathon Bombs Made From Pressure Cookers

The FBI has revealed that one of the Boston Marathon bombs appears to have been made from a pressure cooker containing nails and ball bearings, NBC News reports.

Investigators have found fragments of dark nylon, possibly from a backpack containing the bombs, as well as pieces of what they believe was a pressure cooker used to make the bomb. Typically, a pressure cooker is used to speed cooking by creating a tight seal which builds pressure inside the pot. A pressure-cooker bomb was used in the 2010 attempted Times Square attack, as well as in Mumbai, India, in 2006.

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Richard DesLauriers, the special agent in charge of the FBI's Boston office, said that the evidence was being sent to Quantico, Va., for testing.

"It appeared to be built from scratch, but with a sophisticated triggering mechanism. And frankly, at the end of the day, all bombs are crude devices, and it is the way they are triggered that can be sophisticated," one official told NBC News. "They functioned as designed."

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"Someone knows who did this," DesLauriers added. "Importantly, the person who did this is someone's friend, neighbor, coworker or relative. We are asking anyone who may have heard someone speak about the marathon, or the date of April 15, in any way that indicated that he or she may have targeted this event to call us." More than 2,000 tips had been sent in as of Tuesday, in addition to photos and video of the area where the bombs went off.

So far the range of suspects and motives remains wide open, the FBI said.