US authorities have released the first pictures of the explosive devices used in the twin blasts which hit the Boston Marathon on Monday.
The images show twisted pieces of a metal container, wires, a battery and a small circuit board which exploded close to the finish line at the race.
In another, a piece of charred wire can be seen attached to a small box and a twisted metal lid with bolts.
The FBI said on Tuesday that a pressure cooker may have been used to build the bombs, with nails, ball bearings and other metal packed around the explosive.
