If you are a prosecutor, you really look for evidence of what the former president did personally. If the DOJ either knows about or is soon to interview those people who were sources for The New York Times, they’re going to have a substantial criminal case.
It's pretty amazing that a former President of the United States of America is on a rat hunt for who gave him and the stolen classified documents up to the feds.
The FBI wasn't after all the money laundering going on, the Don jr, baby powder everywhere, the dead bodies hidden in the walls, or the secret torture chambers where all the rats end up.