Colonel Stig Wennerström was arrested in 1963 on suspicion of espionage while he was working as a military expert for the disarmament negotiator Alva Myrdal.
He was sentenced the following year to life imprisonment for spying on behalf of the Soviet Union. Wennerström’s Soviet codename was ‘Örnen’, the eagle.
Wennerström had been involved with the Soviet intelligence services since 1948, when he was appointed air force attaché in Moscow. He exposed the whole Swedish military system to the Soviets, with special emphasis on the air defence system.
He also revealed that Sweden had a major signal tracking agreement with the United States, a cooperation which contradicted the country’s public neutrality policies.
The damage he caused to the Swedish military was valued at tens of millions of kronor.
Towards the end of his time in jail, much of which was spent in solitary confinement, he worked as a language teacher at a juvenile detention centre.
In September 1974, at the age of 68, he was released due to good behaviour and returned home to his wife in Djursholm.
In an interview for the magazine Året Runt in 2003 he said that he became a spy out of loyalty following his friendship with the Russian diplomatic corps.
Other reports since his imprisonment say that the real reason was that the Russians knew he had spied for the Nazis during the Second World War and threatened to reveal this if he did not spy for them.