The Double (2011) on Netflix

When a senator is murdered, CIA agent Paul Shepherdson that is near retirement is summoned by his chief Tom Highland to investigate the murder of a senator. Paul has joined CIA twenty-five years ago and has been unsuccessfully hunting down the Russian assassin Cassius 7. The senator was murdered with the same "modus operandi" of Cassius 7, but Paul insists that it is a copycat. They go to a meeting with the FBI and Paul is introduced to the young FBI agent Ben, who has prepared his Harvard thesis based on the killer. Tom asks the reluctant Paul to work with Ben to find Cassius 7 whereabouts. But the problem is Paul Shepherdson is Cassius 7 and Ben knows too much about the assassin.