History's Greatest Mysteries 7 19 11928375 2026-08-31 Deadly anthrax spores sent through the mail kill five people and spread authorities thin. The FBI works around the clock to stop this brazen act of bioterrorism, but the letters keep coming. 42 7 19 https://artworks.thetvdb.com/banners/v4/episode/11928375/screencap/6a91055136339.jpg