Mysterious deaths in Soviet Russia and what they might tell us about the origin of Covid.

When US intelligence agencies blamed a spate of unexplained Russian deaths in 1979 on a leak from a bioweapons facility, the Soviet government responded angrily, saying the cause was natural. A top US scientist stepped in to find the truth - and was given anything but. Does pointing the finger of blame creative a disincentive for governments to cooperate more fully? Or should information from inside authoritarian states be treated with suspicion? A Chinese insider has a set of striking revelations and someone who dismissed conspiracy theories now has one of his own.

Archive: CBS; The White House; C-SPAN; New Yorker; New York Times.

Presenter: John SudworthSeries producer: Simon MaybinEditor: Richard VadonSound design and mix: James BeardCommissioning editor: Dan ClarkeScience advice: Julian Siddle and Victoria GillExtra production: Eva Artesona and Kathy LongResearch support: Zisheng Xu and BBC MonitoringProduction coordinators: Siobhan Reed, Helena Warwick-Cross, Sophie Hill, and Debbie RichfordTheme and original music: Pete Cunningham, with trumpet by Joss MurrayRadio 4 Editor of Editorial Standards: Roger MahonyHead of BBC News - Long Form Audio: Emma Rippon