I don’t have any idea. But suggest you read the New Yorker article (link in this article).
Somebody is protected (Comey??) or has huge brass balls.
Did Mueller give Comey total immunity? Can he extend that beyond the reach of the Special Prosecutor. Protection generally is given for existing crimes. Not for illegal leaking highly sensitive data like this.
I don’t think immunity would cover future crimes. This leak would have to be after any immunity deal.