Robert Hansson, was giving information for 15 years. He is the highest ranking agent that I know that was helping the Soviets.

Earl Pitts, was giving information for 5 years, and possibly techniques and procedures of FBI protocol when he became an instructor.

There was an FBI informant who was also giving the KGB information of nearly 30 years. I think he is the one you might be thinking of Furio.

"I have this Nightmare. I'm on 5th avenue watching the St. Patrick's Day parade and I have a coronary and nine thousand cops march happily over my body." Chief Sidney Green