Sweden has revealed that it uncovered a network of informers during the 1990s that had supplied information to East German secret police in the Cold War.
The Stasi informants sent information back to East Germany
Sapo, the security service branch of Sweden's police force, said it found 50 spies who had worked for the Stasi.
Prosecutions were brought against a number of the informers on the list but the charges were thrown out because too much time had passed.
Sapo divulged the spy list's existence following media requests.
The revelation came after the publication in June of a book about Stasi espionage in Sweden, a country that was neutral during the Cold War.
Swedish intelligence identified the spies between 1993 and 1995 during investigations launched after the Berlin Wall fell in 1989.
Anders Thornberg, head of information at Sapo, told the BBC News website: "We questioned all the suspects and brought prosecutions in a number of cases.
"They were charged with unlawful spying but the cases were thrown out because more than five years had elapsed since the time of the offences.
"These cases are all closed. We will not reveal the names."
Investigative journalist Bjorn Cederberg, the author of Kamrat Spion (Comrade Spy), the book about the Stasi espionage network, said he was now considering whether to mount a legal challenge to force Sapo to identify the informers.
He told the BBC News website: "After looking through the Stasi files in Berlin, I found the informers' codenames but not their identities.
"At least one informer on the list had access to top secret information about Sweden's military.
"The Stasi were interested in Sweden because it was neutral but had some co-operation with Nato and they wanted to find out its real position."