Most probably a mole. If Hanssen was a spy, it seems he planned for everything except a double agent like himself in Russian intelligence who would one day betray him. And that means to be the perfect spy, you have to be the perfect spy for a long period of time. Not just once. And the longer he does it, the better the rush.
Nothing lasts forever.
That was 15 years ago. The day he was arrested Hanssen was weeks from retirement. He would never meet the man who employed so many American spies. The Cold War has ended but the spying continues. I appreciated your efforts.