A lid to a pressure cooker thought to have been used as the explosive device in the Boston bombings has been found on a roof of a building near the scene.
Take a look at the device fragments and other crime scene images from the deadly bombings.
Investigators prepared to survey the scene of the bomb blasts on Boylston Street in Boston.
Investigators surveyed the scene took pictures of the remains of an explosive device at the site of the bomb blast.
The bombs, which exploded 12 seconds apart, killed three people and wounded 183.
One was housed in a pressure cooker hidden inside a backpack, the FBI said in a joint intelligence bulletin.
Investigators say that the trigger mechanisms of the Boston marathon bombs were battery powered.
Destroyed electronic board parts lie on the ground around the scene of the detonation of one of the bombs.
The device also had fragments that may have included nails, BBs and ball bearings.
Pieces of the sophisticated detonator were found on the scene.
More remains of what are thought to be pressure cooker bombs.
To view a timeline of the events in the Boston Marathon explostions, click here.