Chasing scientific renown, grant dollars, and approval from Dr. Anthony Fauci, Peter Daszak transformed the environmental nonprofit EcoHealth Alliance into a government-funded sponsor of risky, cutting-edge virus research in both the U.S. and Wuhan, China. Drawing on more than 100,000 leaked documents, a V.F. investigation shows how an organization dedicated to preventing the next pandemic found itself suspected of helping start one.