Officials survey the roof of Lord & Taylor department store in Boston
Officials survey the roof of Lord & Taylor department store, three days after two explosions hit the Boston Marathon, in Boston, Massachusetts April 18, 2013. President Barack Obama told a memorial service for the Boston bombing victims that "we will find" whoever carried out the attack that killed three people as investigators search for two men seen on a video of the scene shortly before the blasts. Though no arrests have been made in the Boston Marathon bombings, media reported that authorities are interested in at least one person shown on CCTV footage taken from a Lord & Taylor department store. REUTERS/Shannon Stapleton (UNITED STATES - Tags: POLITICS CIVIL UNREST)