The FBI has released images of what they say is one of the devices that exploded at the Boston Marathon Monday.
Investigators say the photos show the remains of a pressure cooker that contained a bomb.
Another photo shows a shredded black backpack and what appears to be metal pellets or ball bearings.
A Boston law enforcement source says two identical pressure-cooker bombs -- each with the capacity to hold six liters of liquid -- were set off.
The FBI says they contained BB-like pellets and nails, causing even more damage.
Three people were killed and more than 180 injured in the attack.
13 of the injured had limbs amputated.