Thanks Delta. That explanation makes sense. Another thing that always puzzled me was in Godfather II - why was Frankie Pentangeli still getting special treatment from the FBI after he didn’t rat out Mikey at the Senate hearing. Seems to me that after that happened, they’d let him rot in jail forever.
Frankie was still the only high level mob boss who had been willing to rat Michael out. By keeping Frankie sequestered was the only leverage that the government had against Michael.
Eventually, the Fed would have tried to understand why Frankie had reneged on his testimony and would have attempted to overcome the obstacles and have Frankie testify against Michael in the future. Not being a court of law, double-jeopardy was not an issue.
This is why even though Frankie recanted before congress, Michael still wanted him dead to prevent him from testifying at some future time.