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.
President Barack Obama said Tuesday the bombings were an act of terrorism but investigators do not know if they were carried out by an international or domestic organization, or perhaps by a "malevolent individual."
