Stig Bergling, a former Swedish security officer who spied for the Soviet Union during the Cold War, has died. He was 77.

Bergling's death was first reported Thursday by Swedish newspaper Dagens Nyheter. The Swedish tax authority, which records deaths, confirmed he died on Jan. 24. No cause was given.

Bergling, who changed his surname several times — it was Sydholt when he died — was arrested in 1979 and sentenced to life in prison for selling defense secrets to the Soviets.

He fled while on leave in 1987, prompting a debate over Sweden's liberal prison system and the resignation of the justice minister.

After seven years on the run Bergling returned to Sweden, saying he was homesick. He was released in 1997 after serving a total of 12 years.