By Peter Finn, Greg Miller and David A. Fahrenthold • Washington Post
Investigators are convinced that the explosive devices that killed three people at the Boston Marathon were not in place before the race began because of security sweeps. And they have focused on increasingly narrow slices of the five-hour window between when the marathon started and the blasts occurred, officials said.
This methodical dissection of terabytes of video, still images and other evidence led the FBI to images of a potential suspect Wednesday. The apparent breakthrough illustrates how private surveillance equipment, in combination with the cellphone cameras used by ordinary citizens, has become an extraordinary resource that allows investigators to re-create the visual narrative of the streetscape surrounding a location in order to scrutinize the hours, minutes and seconds ticking down to a crime.
'Just a matter of finding it'
"There is absolutely going to be video of almost every single inch, for every single second of that day; it's just a matter of finding it," said Andrew Obuchowski, a former Massachusetts police officer who analyzes video evidence for Navigant Consulting, a private firm.
Video has proven crucial to a number of high-profile international investigations in recent years. In Dubai in 2010, the suspected assassins of a senior figure in the Palestinian group Hamas were captured on hallway video cameras in the hotel where the target, Mahmoud al-Mabhouh, was staying. In London in 2006, the city's cameras were used to trace the movements of Alexander Litvinenko, a former Russian agent, on the day he was poisoned.
Along with the forensic examination of residue from the bombs, U.S. officials said, investigators are focusing heavily on the enormous volume of video footage and images taken by security cameras and spectators and turned over to the FBI.
The bureau's website offers instructions on how to submit footage of interest in the investigation, and the effort to gather it is so extensive that security officials at Logan Airport have been asking travelers leaving Boston whether they have data that could be useful.
Officials said they are organizing the video footage and digital images according to precisely where and when they were taken, relying on an array of clues to determine locations along the race route and the time that specific pictures were snapped. The fact that the bombing occurred at a marathon — an event that records runners' finish times in fractions of a second — has aided the effort. Investigators have used the numbers worn by runners to determine their finish times and then extrapolated backward to determine when they crossed key landmarks. Pictures taken by cellphones also typically have time stamps and, in some cases, GPS location data.
