PHOTOS A look inside one of the Boston bombs
Boston Bomb 1
The FBI says it appears one of the bombs used in the attack at the Boston Marathon was housed in a pressure cooker hidden inside a backpack.
Boston Bomb 2
To maximize the impact of the shrapnel, the device may have included nails, BB's and ball bearings.
Boston Bomb 3
The FBI says the second bomb was also housed in a metal container, but there's not enough evidence to determine whether it was also in a pressure cooker.
Evidence recovered from the scene will be sent to the FBI's lab in Quantico, Virg., where analysts will reconstruct the devices used in the attack.