For at least two years in the late 1970s, the ASIO mole was the feared Russian spy agency's only back door to American and British intelligence secrets.
Some longtime officers like Peacock, known in the service as "the old and bold", were frustrated, believing the organisation had lost direction.
Peacock's career seemed to have plateaued as a new breed of tertiary-educated officers moved up through the ranks.
At its peak, the Cold War played out not on a conventional battlefield but in the shadowy world of adversarial spy agencies.
The Soviets were desperate to learn the secrets of the Five Eyes intelligence alliance members: the US, UK, Canada, Australia and New Zealand.
This mistake clouded the spy agency's judgement for the next decade, even when there were further intelligence indications that it was an ASIO mole.
The details of ASIO's hunt for the mole, and any successor he may have found for the KGB, have remained closely guarded. »
