The Justice Department is investigating whether senior FBI officials mishandled classified materials tied to the bureau’s Russia probe.

A source confirmed to CBS News that the documents were discovered inside “burn bags” at FBI headquarters, containers usually reserved for destroying sensitive files. The materials are connected to Crossfire Hurricane, the FBI’s 2016 investigation into possible ties between Donald Trump’s campaign and Russia.

FBI Director Kash Patel said last month that thousands of Russia-related files were uncovered in the bags, which he claimed had been hidden.

Patel later wrote on X, “We just uncovered burn bags/room filled with hidden Russia Gate files.”

The FBI opened Crossfire Hurricane during the 2016 campaign and continued it into Trump’s first term. Former Justice Department special counsel Robert Mueller concluded Russia interfered in the election with the goal of helping Trump. Mueller did not accuse Trump or his aides of criminal coordination with Moscow.

A 2017 intelligence community report also found Russia sought to influence the election and developed a preference for Trump. Those findings have long been challenged by Trump and his allies, who have called the probe a hoax and a witch hunt.