STORY: A doping scandal surrounding Chinese Olympic swimmers is heating up, as the United States anti-doping chief on Monday demanded a probe into global regulator WADA's handling of the matter.While WADA itself threatened legal action over accusations of a potential cover-up.Named the World Anti-Doping Agency in full, the regulator confirmed on Saturday that some Chinese swimmers had tested positive for a banned drug several months before the Tokyo Olympics in 2021.It came after some media reports alleged a cover-up, which WADA called "misleading".The agency has since come under fire, after saying it accepted China's findings that the positive tests were due to environmental contamination, not intentional doping."We had no evidence of wrongdoing..."On Monday, WADA officials hit back at critics during a video press call, explaining in detail why it did not punish the swimmers, who tested positive for a substance found in heart medication known as TMZ. WADA General Counsel Ross Wenzel said one of the key factors that point to contamination was the lack of a concrete positive result of TMZ across multiple tests."So positive, negative, positive, negative, negative, positive. And always at these low levels... Ultimately these fluctuating negative-positive results were not compatible with deliberate ingestion, not even microdosing.”The Chinese team won six medals at the Tokyo Games, including three golds.A report by China's doping agency CHINADA determined that all the swimmers in question were staying at the same hotel where traces of TMZ were found in the kitchen, the extraction unit above the hall and drainage units.Though it gave no explanation for how the TMZ might have found its way into the hotel.WADA said it could not conduct any investigations on the ground, due to COVID restrictions at the time.Instead, it relied on CHINADA's report, then hired their own scientific and legal experts who tested and accepted the contamination theory.WADA officials insisted there was no cover-up and said it would consider legal action against such claims.China's foreign ministry spokesperson on Monday also refuted the media allegations as "false".But pressure is mounting from international athlete groups, who are questioning why China was allowed to investigate itself.U.S. Anti-Doping Agency CEO Travis Tygart is pushing for a probe into the case."We have to get to the bottom of how this possibly happened and more importantly, be sure going into 2024, that athletes that, you know, had these positive tests, you know, some sort of justice occurs so we can have some finality." Ahead of the Paris Olympics this summer, Tygart said it's crucial to clear the matter up, not only so athletes will compete fairly, but also without these doubts lingering in their minds.