Disenchanted by the lackadaisical attitude of fellow FBI agents, Hanssen approached Russian agents and offered to sell secret documents. He was rewarded famously for his efforts but was caught by his wife while counting $20,000 and writing a letter to the Soviets in his basement. Thinking he was writing a love letter to a girlfriend, she demanded to know what was going on. He admitted to her where he had gotten the money but claimed that he had only given the Soviets useless information. Instead, he had actually provided the Soviets with very valuable information , including the identity of Dmitri Polyakov, a top-level Soviet double-agent. Rather than turn him into the authorities, she convinced him to confess his actions to an Opus Dei priest. The priest instructed him to give up his activities and to donate the money he received to Mother Theresa's charities.

Was considered a highly intelligent agent, but his tepid interpersonal skill as well as his continued preference for black suits caused many to tag him with the nickname "the Mortician." Unfortunately, the perception that he was an aloof, introverted worker hindered his upward mobility within the Bureau. Was transferred to the FBI headquarters in Washington, DC where he was initially assigned to develop a budget for the Bureau that was to be presented to Congress. Was moved to the Soviet Analytical Unit in 1983 and given a high security clearance. After a four year stint, was transferred back to New York.

Decided to re-establish his link to the Soviets. Knew that the FBI was not conducting surveillance on Victor Degtyar, a KGB Colonel living in Alexandria, Virginia. Hanssen therefore sent a letter to Degtyar, with instructions to pass another letter on to Victor Cherkashin, the head of Soviet espionage efforts in Washington. In this letter, Hanssen offered to turn over classified and highly sensitive information to the Soviets in return for $100,000. He also provided the name of three Russian agents who were working for the United States. Two of the agents were executed and one was imprisoned.