The two bombs that exploded through crowds at the Boston Marathon, killing three people and wounding more than 170, were fashioned out of pressure cookers and packed with shards of metal, nails and ball bearings, a person briefed on the investigation told The Associated Press on Tuesday. The details of the explosion emerged as investigators appealed to the public for amateur video and photos that might yield clues, and the chief FBI agent in Boston promised to "go to the ends of the Earth" to find those responsible.

A person who spoke to the AP anonymously as the investigation continues said that the explosives were put in 6-liter pressure cookers, placed in black duffel bags and left on the ground. They were packed with shrapnel, the person said.

The person said law enforcement officials have some of the bomb components but do not yet know what was used to set off the explosives. A doctor treating the wounded victims appeared to corroborate the person's account early Tuesday morning, saying one of the victims was maimed by what looked like ball bearings or BBs.