The publication is a co-production with the British BBC, Danish DR and Norwegian NRK and the project is one of the most difficult that Axel Arnö, project manager at Dokument utfra, has worked with.

- It has been one of the most complicated jobs I have landed.

A lot because it has been so secret all along, says Axel Arnö.

In the documentary, we get to follow the Dane Ulrich Larsen, who acted as a mole in the North Korean Friends Association in Denmark, and how he eventually advanced in rank and was able to receive drawings of an underground weapons factory on an island in Uganda, at the North Korean embassy in Stockholm.

- He is a fairly everyday figure, who perhaps wanted a little excitement in his life, joined a North Korean friends association in Denmark.

Then he rises in the ranks and becomes one of the highest representatives of the International Friends Association.

- Then he comes close to someone who has direct contact with Kim Jong Un, and then things start to happen.

Watch Axel Arnö talk about the work with the documentary in the clip above.