I would prefer for them to be required to go on record as to how they received the information.
Simple answer - polygraph and interview every single person who had access to the files.
Every single one.
This was a felony leak. Period. Given the highly unusual and partisan nature of the seizure of these materials it should be fully investigated and people should be suspended pending the investigation.
The judge needs to authorize a pre-dawn no-knock raid on the offices and homes of the NYT editors, The FBI team that raided Projecr Veritas, and everyone in the FBI up to and including Fay Wray.