This is Death in Ice Valley, an original podcast series from the BBC World Service and NRK.

Although the much-loved seabird that the Amtartic lives in the southern hemisphere, in the 1960s

and the 1970s, its namesake was taken to the skies off the Norwegian coast, way up north.

And the Russians were watching, closely.

Episode 5, The Penguin.

I am Mordetegraff.

And I'm Neil McCarthy. Now, Marit, you've been examining this case closely for a couple of years now,

trawling through police files and talking to witnesses, but there's one place that took a lot

of perseverance to get into. The Secret Police Archive.

Yes, that's right. It guards its secrets well. But along with my colleague, Stola Hansen, who's

the documents expert on the case, we were granted permission to look at the secret filed of the Easter woman.

Well, we're here at the Secret Police in Norway holding the secret file of the Easter woman.

We see here their marked with secret. Yes, that's the classification from 1970 and secret.

In the Norwegian system, it's the second highest classification.

The first document here is marked by the Beringen-Pultighamme, the police in Bergen.

So they are also documents that we have in the police investigation file.

So there aren't very many documents here that are actually produced by the counterintelligence police.

How was it to be inside the secret police archive?

It was exciting to look inside the file, especially since journalists hadn't been allowed to see it for so long.

We had high expectations that we'd find some hidden secrets inside, but we're surprised that it was a very thin file,

which didn't seem to offer us much.

But there was one very interesting classified document.

...