An investigator hired by the global antidoping regulator found no bias toward China in a case that has outraged Olympic athletes and led to an F.B.I. investigation.

After a spate of positive tests for performance-enhancing drugs by athletes, the World Anti-Doping Agency is investigating why China and other countries are citing contaminated food as an explanation.

Two Chinese athletes, one of whom was named to the Olympic team in Paris, tested positive in 2022 for a banned steroid. China blamed contaminated food, as it had after previous positive tests.

Olympic officials insisted on the right to pull the Games amid U.S. investigations into how the World Anti-Doping Agency handled positive tests for banned substances among Chinese swimmers.