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.

The agency, which has faced intense criticism for its handling of positive tests among Chinese swimmers, should be replaced by a “truly independent” organization, its former chief investigative officer said.

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.

A special prosecutor said the decision not to pursue punishments against a group of Olympic swimmers was “indisputably reasonable,” even though agency scientists had expressed doubts.

Lawmakers expressed openness to withholding funding from the agency after reports that Chinese swimmers were allowed to compete in the 2021 Games after testing positive for a banned drug.