How federal and local investigators sifted through that ocean of evidence and focused their search on two immigrant brothers is a story of advanced technology and old-fashioned citizen cooperation. It is an object lesson in how hard it is to separate the meaningful from the noise in a world awash with information.
The killing of Tamerlan Tsarnaev and the capture of his younger brother, Dzhokhar, may seem like an inevitable ending given that their images were repeatedly recorded by store security cameras and bystanders' smartphones. But for 102 hours last week, nothing seemed certain in the manhunt that paralyzed a major metropolis, captivated the nation and confronted counterterrorism operatives with the troubling and unforgiving world of social media and vigilante detective work.
While the analysts combed through videos frame by frame, a more traditional tip was developing two miles away at Boston Medical Center. Jeffrey Bauman, groggy from anesthesia, his legs just removed at the knee, managed to eke out a request for pen and paper.
In the intensive-care ward, Bauman, who had been near the finish line to see his girlfriend complete Monday's race, wrote words that would help lead to quick resolution of the bombings that killed three and injured 176 others: "Bag. Saw the guy, looked right at me."
FBI agents quickly came to Bauman's bedside. A man in sunglasses and black baseball cap had walked right up to him, placed a black backpack on the ground and stepped away, Bauman remembered.
His tip became a critical lead, according to law enforcement officials.
Of course, investigators had 2,000 other leads, too, in the form of photos and video that "almost became a management problem, there was so much of it," said Davis, who led the local piece of the probe from a ballroom at the Westin Hotel where 100 officers and commanders from local, state and federal law enforcement collaborated. The room was equipped with tables for laptops, power strips and, most important, land lines, since cellphones were unreliable in the chaos after the bombings and satellite phones worked only if you stood by a window.