Heavy documentation of Boston Marathon is an asset to investigation

Boston authorities repeatedly urged the public to come forward with any information or media that may offer leads into the Boston Marathon bombings during a press conference Tuesday. Police chief Ed Davis offered an update that 176 people are inured, 17 critically, as a result of the explosions. (The Washington Post)

For all the horror of the Monday bombings in central Boston, investigators have been blessed with at least one advantage: a rich stream of possible evidence drawn not only from surveillance cameras but from personal photos and video footage, as well as cellphone records.

Authorities on Tuesday said that they planned to sift through footage from surveillance cameras near Boston’s Copley Square and that police had been assigned to review surveillance tapes from nearby businesses. The commissioner of the Boston Police, Ed Davis, vowed officials would go “through every frame of every video” taken during Monday’s Boston Marathon.

“This is probably one of the most photographed areas in the country yesterday,” Davis told reporters.

Investigators said they had already received a huge volume of tips, but appealed to the public to share any amateur photos or videos they might provide clues. Officials have said they do not have any suspects.

“There have to be hundreds if not thousands of photographs or videos or observations that were made down at that finish line yesterday,” said Col. Timothy Alben, superintendent of the Massachusetts State Police.

“I would encourage you to bring forward anything,” he said. “You might not think it’s significant, but it might have some value to this investigation.”

A federal law enforcement official said the FBI is also checking cellphone activity on towers near the scene of the blasts. Experts say that data could be particularly useful if the explosives were detonated by phone, especially since they know the exact time the blast occurred.

“Get a dump for the closest tower and look for all calls or texts terminating at the bomb site from 2:49 to 2:50 p.m.,” said Michael Sussmann, a former federal prosecutor who now represents wireless providers as a partner at Perkins Coie law firm in Washington. “If there are many, it will be a one to five second call, so look for short calls. Then correlate with the other blast site and see if the incoming number at the time of the second blast matches.”

If the tower data yield suspect numbers, investigators can obtain from the phone company subscriber information giving name, address and billing information. If the phone was a disposable model, it’s possible to learn where the phone was purchased. Surveillance cameras near the point of sale could provide further clues, some former federal prosecutors said.

If the bomber used two different cell phones, then that makes tracking them back more difficult.

In general, cell tower data will be more useful once investigators have a lead on a suspect. But collecting that data now makes sense to have it on hand to sift through later, officials said. Each clue is a piece to a jigsaw puzzle, and the tower records may have that piece that later helps the picture become clear.

Vernon Loeb in Boston and Sari Horwitz in Washington contributed to this report.

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