Police were in a desperate race against time to find any additional devices and said the task had been complicated by the items discarded by spectators fleeing the scene.
Multiple reports were flooding in in the moments after the attack, saying there were devices reported outside Harvard and other sites along the marathon route. But today it was confirmed that there were only two devices.
Massachusetts General Hospital, where 22 victims of the bomb blast are being treated, was forced into lock-down for about two hours after a suspicious package was reported in the parking garage across the street.
Bomb sniffing dogs from the Rhode Island State Police, SWAT officers from the Boston police department and bomb squad officers searched the entire parking structure, floor-by-floor
Authorities found one bag, but determined it was not a threat and contained nothing suspicious.