<p>Mysterious deaths in Soviet Russia and what they might tell us about the origin of Covid.</p><p>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.</p><p>Archive: CBS; The White House; C-SPAN; New Yorker; New York Times.</p><p>Presenter: John Sudworth
Series producer: Simon Maybin
Editor: Richard Vadon
Sound design and mix: James Beard
Commissioning editor: Dan Clarke
Science advice: Julian Siddle and Victoria Gill
Extra production: Eva Artesona and Kathy Long
Research support: Zisheng Xu and BBC Monitoring
Production coordinators: Siobhan Reed, Helena Warwick-Cross, Sophie Hill, and Debbie Richford
Theme and original music: Pete Cunningham, with trumpet by Joss Murray
Radio 4 Editor of Editorial Standards: Roger Mahony
Head of BBC News - Long Form Audio: Emma Rippon</p>
