Russian intelligence officials believe that if U.S. authorities had acted on warnings about Tamerlan Tsarnaev, the Boston Marathon bombings could have been prevented, U.S. Rep. William Keating said Saturday after returning from a congressional delegation trip to Russia. The Massachusetts Democrat, who met with Russian intelligence officials Thursday, said he was provided with details on how U.S. intelligence agents were warned in 2010 that Tsarnaev was preparing to join a terrorist cell in the southern Russian region of Dagestan, the Boston Globe reported. Keating told reporters at Boston's Logan International Airport that a top Russian counterintelligence official told the delegation...