The Department of Justice's investigation into the Federal Reserve and Chairman Jerome Powell quietly began late last year amid President Donald Trump publicly intensifying his attacks, three sources with knowledge of the situation confirmed to NBC News.

The probe reportedly began in November and the U.S. Attorney's Office for the District of Columbia reportedly didn't contact main Justice Department officials, the White House or the Treasury Department when subpoenas were ready to be issued, the three sources, who spoke on the condition of anonymity, confirmed. Trump said he was unaware of the Department of Justice subpoenaing the Federal Reserve and threatening to indict Powell while speaking to NBC News during a brief interview Sunday (January 11) night.

“I don’t know anything about it, but he’s certainly not very good at the Fed, and he’s not very good at building buildings,” Trump said when asked of the subpoena and threat to indict Powell.

Powell announced that the U.S. Department of Justice served the Federal Reserve with grand jury subpoenas threatening a criminal indictment against him related to his testimony before the Senate Banking Committee last June in a statement and video message shared Sunday night.

“No one — certainly not the chair of the Federal Reserve — is above the law,” Powell said. “But this unprecedented action should be seen in the broader context of the administration’s threats and ongoing pressure.”