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You're listening to the documentary from the BBC World Service.

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This is the fifth floor, at the heart of global storytelling with BBC journalists from all around the world.

I'm your host, I'm your host, I'm Renata Taranuk.

In April 2022, two months after Russia invaded Ukraine, a man in his 30s called Viktor Mullah Ferre

flew in to Amsterdam airport using a Brazilian passport. He was identified by the Dutch

authorities as Russian national Sergei Vladimir Cherkassov,

and immediately sent back to Brazil, where investigations by both the FBI and the Brazilian

police identified him as a Russian intelligence officer. He is currently serving a five-year

prison sentence in Brazil for identity fraud.

With me on the line from Brasilia is Leandro Praseres, who has been covering the story for BBC News Brazil

and from London, Olga Ifshina of BBC Russian.

I began by asking Leandro to set out what is known about Sergei Cherkasov.

What we know is what the Brazilian authorities and also the US authorities have been saying is that

Turkasov, it's a special type of spy called illegal.

These guys, they are sent overseas to blend in and build a completely fake identity and personality

...