The Federal Bureau of Investigation has released photos of debris from one of the bombs used in the Boston Marathon attack.
Authorities say the bombs were made from 1.6 gallon kitchen pressure cookers packed with explosives, nails and other lethal shrapnel.
Although the White House has called the attack an "act of terrorism" officials still don't know who carried out the bombing nor why.
Investigators also found pieces of black nylon from a bag or backpack that may have held a pressure cooker bomb.
These items have already been sent to the FBI lab in Quantico, Virginia for analysis.