This image from the FBI shows a fragment of one of the homemade bombs used in the attack at the finish line of the Boston Marathon on Monday. The explosives are believed to have been housed in a pressure cooker.
An intelligence bulletin issued to law enforcement includes pictures of a mangled pressure cooker and a torn black bag that the FBI says were part of a bomb that exploded during the Boston Marathon.
The bulletin was obtained by NBC News and The Associated Press.
The FBI says it has evidence that indicates one of the bombs that exploded in the Boston Marathon was contained in a pressure cooker with nails and ball bearings, and it was hidden in a backpack.
The FBI says the other explosive was in a metal container, but there wasn't enough evidence to indicate that it was a pressure cooker.
It was not known what was used to set off the two explosives that killed three people Monday and injured more than 170 others.
Many other questions were left unanswered late Tuesday, too, NBC News reported — among them questions of whether a single individual were responsible for planting the bombs, what motivated the attack, why nobody had claimed credit and when the bombs were placed.
The photograph above shows what the FBI says is a torn black bag it believes contained one of the bombs detonated at the Boston Marathon on Monday.