A person briefed on the Boston Marathon investigation says the explosives were in 6-liter pressure cookers and placed in black duffel bags.

The person says the explosives were placed on the ground and contained shards of metal, nails and ball bearings. The person spoke on the condition of anonymity because the investigation was ongoing.

The person says law enforcement officials have some of the bomb components but did not yet know what was used to set off the explosives.