The FBI has urged the public to help as its hunt for the perpetrator of the Boston Marathon bombing enters a third day. An appeal for information has already yielded more than 2,000 tips and the FBI—which has released photos and details of the bombs that killed three and injured more than 170—has appealed for photos, videos, or any other information that could help them as they build a clearer picture of their target, the AP reports. Officials say nobody is in custody and it's not clear whether a group or individual is responsible.
"The person who did this is someone’s friend, neighbor, or relative,” says the FBI's special agent in charge in Boston, describing the range of suspects and motives as wide open. “Someone knows who did this." More than a thousand investigators are analyzing photos and videos and speaking to witnesses, the Boston Herald reports. The picture beginning to emerge from the investigation is that of a suspect or suspects carrying black nylon bags or backpacks, according to Reuters. (Read more Boston Marathon stories.)