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One of the blast sites on Boylston Street near the finish line of the 2013 Boston Marathon is seen in Boston, Tuesday, April 16, 2013, one day after bomb blasts killed three and injured over 140 people. FBI agents searched a suburban Boston apartment overnight and appealed to the public for amateur video and photos that might yield clues to who carried out the Boston Marathon bombing. (AP Photo/Elise Amendola)
Police are painstakenly collecting evidence at Copley Square, the site of the Marathon bombings.
Guests
Tom Nolan, a former police officer, he's now a professor of criminal justice at Boston University.
