These are images of the remnants of a pressure cooker used in one of the devices that exploded during Monday's Boston Marathon, and a black bag used to hide it.

These photos were distributed by the FBI to law enforcement, and were obtained by the Associated Press and Fox 5 Atlanta. Investigators now believe the bombs were homemade devices housed in stainless steal pressure cookers, which can amplify the power of the blast by briefly containing it. The bombs were packed with nails and ball bearings designed to create shrapnel and maximize the carnage.

Similar devices have been used all over the world, and blueprints for building them are readily available online.

Investigators believe at least one of the devices was hidden in a black bag, most likely a nylon backpack.


What appears to be a piece of a circuit board has also been recovered, seeming to indicate the bombs were set off by a timer, not remotely detonated.

The FBI is urging anyone with information to call them at 1-800-CALL-FBI (1-800-225-5324).