That other person later became an FBI source in a criminal probe of foreign political lobbying, which McGonigal was supervising, authorities said.
The former top FBI agent in New York for counterintelligence was arrested with an ex-Russian diplomat and charged with violating U.S. sanctions on Russia after he left the FBI by trying to help the oligarch Oleg Deripaska get off the sanctions list, federal prosecutors said Monday.
McGonigal and Shestakov, 69, who also was arrested Saturday evening, are due to appear in court in Manhattan later Monday.
McGonigal previously had investigated Deripaska, who made his fortune in Russia's aluminum industry, while at the FBI.
McGonigal agreed to help, and told an FBI supervisor who worked for him that he wanted to recruit the Deripaska employee, the indictment says.