LW with all respect I think it is possible that Questadt knew Geary was compromised by Michael, and through Turnbull could have approached him by saying, "We know you have done favors for Michael Corleone, but we have a way for you to get out from under his thumb. When Willie Cicci testified ask him if the family had buffers to make it appear someone other than Michael was ordering the murders of people. We have a witness who will refute this.

Geary through Turnbull would then work out a deal by which Geary would ask that one question and then be allowed to excuse himself from the proceedings to make it appear he had no part in what was being done to Michael, while al the while being the person setting him up. If Michael had been indicted for perjury, then Geary could be in a position to be on Roth's payroll, and have the Michael blackmail behind him.