Speculation that newly declassified US intelligence will contain smoking-gun evidence.

Three years on from the start of the pandemic, the FBI - the US domestic intelligence agency - reveals it sees a lab leak in Wuhan as the most likely source of Covid. Weeks later, the US Congress passes a law requiring the country’s intelligence agencies to declassify information they have that potentially links the Wuhan Institute of Virology with Covid’s origin. What will it reveal? And, in our final episode (for now at least), what conclusions can we reach about that question that’s sparked so much controversy and acrimony: where did Covid come from?

Archive: Fox News; C-SPAN.

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