The Russian journalist and Cambridge-educated historian Vladimir Kara-Murza has been a long-time opponent of President Putin's regime. A dual national who also holds a British passport, he was instrumental in getting the Magnitsky Act passed in now over 30 countries, in a campaign led by financier Bill Browder. The legislation enables governments to sanction Russians engaged in corruption or human rights abuses. He has been a thorn in the side of Putin ever since. More recently he has also spoken out against Russia's war in Ukraine.

He was poisoned in Russia, and almost died, twice, in 2015 and 2017, suffering long-term health consequences. Yet he returned to Moscow from the US last year, because he didn’t think he had any right to call people onto the streets into action in Russia if he was sitting safely in America. He was arrested soon after his return, and this week was sentenced to 25 years in a Russian penal colony.

But as he wrote from prison: 'the night is darkest before the dawn, but what do you know, the dawn may be just around the corner.' His friends however fear for his life.

Presenter Mark Coles speaks to some of those who know him best: Bill Browder, the head of the global Magnitsky Justice Campaign; University of Cambridge historians Dr Clare Jackson and Prof Hubertus Jahn; fellow Russian opposition figure Vladimir Milov, and the BBC's former Moscow correspondent Sarah Rainsford.

Producers: Arlene Gregorius and Georgia Coan Editor: Richard Vadon Sound Engineer: Rod Farquhar Production Coordinator: Maria Ogundele