Trump took ALL of his presidential records instead of turning them over to the National Archives, which brought attention to Trump.
the National Archives for a year after Trump left office requested their return.
in the end of January 2022, Trump finally returned 15 cases of his presidential records.
in February when traffickers began sorting through them to organize for any research or FOIA records requests, found top secret documents mixed in with the Trump presidential records.
NARA protocol was to let the FBI know when classified information is found....
From that point on the FBI was involved in trying to retrieve any other top secret documents Trump may have brought with him.