The Federal Bureau of Investigation tried to recruit Oleg V. Deripaska, a Russian billionaire, as an informant around 2014, hoping he might shed light on organized crime and, later, possible interference in the presidential election.
A decade later, Mr. Deripaska may have turned the tables on the F.B.I.: Prosecutors say the oligarch recruited one of the bureau’s top spy catchers, just as he entered retirement, to carry out work that they say violated U.S. sanctions.
