“I am pretty sure any immunity offer would have to be approved by DOJ. Mueller is just a special COUNSEL, not a prosecutor.”
Oh? See:
http://www.freerepublic.com/focus/f-bloggers/3560672/posts
Just to be clear: US Attorneys, and a Special Counsel, have to get approval from DOJ hierarchy and a federal judge to grant formal immunity.
There can be informal deals that might fall under prosecutorial discretion, but that seems unlikely in such a high profile case.
I believe bloggers are making stuff up and FReepers are hyperventilating.
https://www.justice.gov/usam/usam-9-23000-witness-immunity#9-23.100