(Reuters) - Boston Marathon bomb scene pictures taken by investigators and released on Tuesday show the remains of an explosive device including twisted pieces of a metal container, wires, a battery and what appears to be a small circuit board.
A U.S. government official, who declined to be identified, made the pictures available to Reuters.
It was not immediately clear what fresh light the photographs shed on the attack. The official said they were taken by Boston's Joint Terrorism Task Force at the scene where two bombs killed three people and wounded 176 on Monday at the finish line of the Boston Marathon.
One picture shows a few inches of charred wire attached to a small box, and another depicts a half-inch (1.3 cm) nail and a zipper head stained with blood. Another shows a Tenergy brand battery attached to black and red wires through a broken plastic cap.
Several photos show a twisted metal lid with bolts. The FBI said on Tuesday that a pressure cooker may have been used to build the bombs.
Earlier Tuesday, FBI Special Agent in Charge Richard DesLauriers told a news conference that evidence recovered from the crime scene on Tuesday morning would be used to reconstruct the device or devices at the Federal Bureau of Investigation laboratory in Quantico, Virginia.
Among the items recovered were pieces of black nylon that DesLauriers said could be from a backpack used to carry bombs that may have been made with a pressure cooker. One of the pictures showed folded pieces of black fabric among the bomb debris.
The metal container bore a label that was partially readable and a small piece of black fabric was attached, the photos showed.
(Reporting by John Shiffman in Washington; Writing by Daniel Trotta; Editing by Mary Milliken and Eric Beech)