On Friday, three UK-based Bulgarian nationals accused of spying for Russia were found guilty of espionage charges at the Old Bailey in London.

“It begins with a simple request,” Dan Sabbagh, the Guardian’s defence and security editor, tells Michael Safi. “A request from one of the world’s most wanted men.”

“He writes, we’d be interested in a Bulgarian guy working for Bellingcat, Christo Grozev, can we look into this guy? Would it raise too many questions?”

Sabbagh explains how Jan Marsalek, an Austrian-born Russian agent, directed a London-based spy network to target journalists.

Safi also speaks to the Russian investigative journalist Roman Dobrokhotov, who lives in exile in the UK, on his experience being targeted by Marsalek and the spy ring.

Support the Guardian today: theguardian.com/todayinfocuspod