The FBI started investigating while first responders were still rushing to the scene. Within three days -- just 101 hours -- the bombers were apprehended.
FBI agents sifted through 13,000 videos and more than 120,000 photographs, drawn from surveillance cameras and onlookers' cell phones. To sort through the piles of footage, law enforcement turned to new technology that can condense an hour of video into just a minute of playback time.
The method, called video synopsis, was invented by an Israeli company called BriefCam, which counts all the right three-letter agencies as clients. (The FBI declined to comment on the specifics of the Boston investigation.)
Video synopsis works in a variety of ways, but most programs layer actions that occur at the same place at different times, making it possible, for example, to see simultaneously every person who walks in a door on a given afternoon. Other notable inquiries have also used BriefCam, like Norway's national security service after Anders Breivik bombed a children's camp there in 2011.