U.S. authorities put alleged Boston bomber Tamerlan Tsarnaev on two separate watch lists in 2011 after Russian security agencies twice reached out to their American counterparts, raising new questions about missed opportunities to prevent the attack. Russian officials contacted the Federal Bureau of Investigation in March 2011, then reached out to the Central Intelligence Agency in September of that year, citing concerns Mr. Tsarnaev might have been associating with extremists, according to U.S. officials.The FBI has said it interviewed Mr. Tsarnaev and conducted a threat assessment, but found nothing "derogatory" that could prompt further investigation. A U.S. law-enforcement official said...