Article Photos: A look at Boston Marathon bombing, investigation 20/20

In this  Wednesday, April 17, 2013 file photo, investigators comb through the scene of one of the blast sites of the Boston Marathon explosions in Boston.  Three more suspects were taken into custody in the Boston Marathon bombing case, including two college friends of Dzhokhar Tsarnaev who came to the U.S. from Kazakhstan, officials said Wednesday May 1, 2013. (AP Photo/Julio Cortez)