So far, this has been a process crime - lying to the FBI.
The process - the FBI calls in the target, and grills said target for three hours., then releases target.
Target is called in three months later, grilled again, almost verbatim the same questions, asked over and over, in varying order. the target is again released, with the admonition “Don’t leave town”, which is enforced by taking away passport and some other documents.
The FBI calls in the target again two moths later, after scrutinizing the transcripts made of the interviews, and confronts the target with even the most minute discrepancy in the accounts which have been given, if the findings of even irrelevancies do not agree, then the target is “lying”.
And that is the crime, which may be prosecuted in a manner not differentiated from the methods used to prosecute high crimes and treason. But wait, we’ll make a deal. Give us something on your boss, and we will reduce the penalties (maybe), if you gives the good stuff, i.e., something we can jail your boss for.
If they were not the people that would be used to investigate it elsewhere, the FBI could be accused and charged under the RICO statutes.