In 1963, flight colonel Stig Wennerström was arrested.
He had worked as an aviation attache in both Washington and Moscow.
Among other things, he had revealed Sweden's secret ties to NATO.
- Telling the Russians that it was a collaboration between Sweden and America.
That we exchanged information that we had picked up on the signals intelligence, says former national police chief Carl Persson in an interview.
Hear more about Stig Wennerström but also convicted spy Stig Bergling in the clip above.