The explosives used in the deadly Boston Marathon bombing were contained in 6-liter pressure cookers and hidden in black duffel bags on the ground, a person briefed on the investigation told The Associated Press on Tuesday.
One of the explosives contained shards of metal and ball bearings, and another contained nails, the person said.
A second person briefed on the investigation confirmed that at least one of the explosives was made out of a pressure cooker. Both spoke on condition of anonymity to discuss an ongoing investigation.
Two bombs blew up seconds apart Monday at the finish line of one of the world's most storied races, tearing off victims' limbs and leaving the streets spattered with blood and strewn with broken glass. Three people were killed, including 8-year-old Martin Richard, and more than 170 were wounded.
A 29-year-old restaurant manager has been identified as another victim killed in the blast.
Her father said Krystle Campbell, of Medford, Mass., had gone with her best friend to take a picture of the friend's boyfriend crossing the finish line on Monday afternoon.
William Campbell said his daughter, who worked at a restaurant in nearby Arlington, was "very caring, very loving person, and was daddy's little girl." He said the loss has devastated the family.
The third victim was a graduate student at Boston University, the school said.