A former FBI agent who once investigated then President Donald Trump’s ties to Russia is now under investigation for his own relationship with a Russian oligarch, Insider reports. Court documents allege investigators are looking into ties between Oleg Deripaska and Charles McGonigal, who once led counterintelligence at the FBI’s New York City field office. Deripaska is a billionaire oligarch and Kremlin aide who was at the center of allegations in 2016 that Russia colluded with the Trump campaign. The investigation appears to center around McGonigal’s work with a shady consulting firm owned by Deripaska, Spectrum Risk Solutions, which he did not disclose. Failing to disclose it may land McGonigal in hot water with the Foreign Agents Registration Act. Even if cleared of any violations, however, a witness subpoena says prosecutors are also looking into whether McGonigal had ties to the government of Bosnia and Herzegovina, and whether he may have received “payments or gifts” from the governments of Kosovo, Montenegro, and Albania.