Cold war historian Thomas Wegener Friis claims to have uncovered the identity of a Danish man that he says was involved in “serious cases” of subversive activities and espionage against his own country.

Friis said he cannot reveal the man’s identity “for legal reasons”, only saying that he is still alive and is well-known.

The information, according to Friis, was uncovered accidentally in previously unexamined classified documents. The papers related to operations of the East German Ministry for State Security. Better known as the Stasi, the ministry engaged in extensive spy operations against Denmark and other countries during the Cold War.

"I am not a lawyer so I do not know if he broke any laws,” Friis told Jyllands-Posten newspaper. “But this information shocks me. What he did was ugly and hurt Denmark.”

Friis called the find "blind luck". 

"The Stasi was a bureaucracy that produced enormous quantities of paper. If an agent had a relationship with a person of interest or was involved in a specific event a document was placed in a folder. The information was not searchable and was impossible to find unless you knew it was there. I stumbled upon by chance," he said.

Friis believes that the US Central Intelligence Agency has been aware of the information he has uncovered for more than a decade.

"Everything I see suggests that authorities could have had this information 15 years ago,” he said.  “The country would have been better served if it had been handled sooner.”

Friis said he may release the man’s name when he has pieced together more information.

“We have caught some small fish before, but this is a case of a completely different calibre. This is undoubtedly the worse espionage case in Danish history. Sometimes reality surpasses even the wildest fiction,” he said.