This may be one that goes up the court chain. It is extremely difficult to sue a government agency and most individuals can't be sued if they are working for the agency.
I believe he has an excellent case against both the agency and the people and there may be some civil recourse for him also. It is provable I think that they intentionally lied to him and about him, and with any luck, he can prove that they threatened his family.
There's no fix for them except that Congress gets involved, or the courts are involved.
We just had the Ruby Ridge anniversary. We should have clued into the disaster that is the FBI long ago.