Tariq Panja, who reported from London, and Michael S. Schmidt, who reported from New York, both have extensive experience covering doping in sports.
Since the revelation that 23 elite Chinese swimmers tested positive before the 2021 Olympics for a banned performance-enhancing drug, Chinese and antidoping officials have repeatedly defended their decision not to discipline the athletes by invoking scientific analysis.
The officials said the science -- which relied heavily on hastily arranged human trials of the drug in question -- backed up their conclusion that the swimmers were unwittingly contaminated, most likely through food served to them at a hotel where they were staying during a meet.
But an examination by The New York Times of the secret human trials conducted by the Chinese during their investigation into the positive tests and interviews with experts suggests the science is not as clear-cut as the officials have claimed.
The results cited by China have never been made public. But The Times obtained a copy of the research and shared it with five doctors and scientists with expertise in research, antidoping efforts and toxicology.
All five said that the research was not nearly as unequivocal as the Chinese made it out to be.
"Their conclusions are not intellectually honest," said Dr. David Juurlink, the head of the Division of Clinical Pharmacology and Toxicology at the University of Toronto, who reviewed the data. "They make a conclusion that is not backed up by what they found in their study. If you submitted this to a scientific journal worth its salt, that conclusion would be laughed at."
Faced with scrutiny for its handling of the episode and others like it, the World Anti-Doping Agency has cited China's science as it has tried to deflect criticism that it looked the other way when confronting a pattern of positive tests among Chinese athletes.
Doubts about the strength of the conclusions drawn from China's research add to the mounting questions about how the positive tests were investigated and adjudicated. Those questions are central to a Justice Department investigation and a pending decision by the Biden administration about whether to continue funding the World Anti-Doping Agency, known as WADA.
The story of how the Chinese and WADA found themselves under scrutiny began four years ago at a national training meet in China, where elite athletes were preparing for the pandemic-delayed Tokyo Games.
Routine testing found that 23 of the swimmers -- including some who would go on to win medals in Tokyo -- tested positive for trimetazidine, a heart medication. The drug, known as TMZ, helps athletes train harder and recover more quickly.
The levels of TMZ in the swimmers' tests were tiny. But under the rules of international sports, the detection of any amount is considered a positive test, in part because of the possibility that athletes might have largely washed a banned drug from their systems by the time they are tested. In this case, the positive results were immediately entered into a global database managed by WADA.
In the weeks afterward, China's national antidoping organization and China's public security authorities began separate investigations, according to documents.
As part of those efforts, both entities started human trials.
Over several days, 144 volunteers between the ages of 18 and 32 were given varying doses of TMZ and then had their urine screened to see how quickly the substance left their systems.
The results, Chinese authorities asserted, ruled out doping. The data, they said, pointed to an innocent explanation for the positive tests: The swimmers had all ingested the drug accidentally and unwittingly, probably through food contamination.
China offered no reason for how or why a prescription heart medication made its way into food served to a team of elite athletes. But the research results were cited as justification for clearing the swimmers.
Saying it had no evidence to challenge the Chinese conclusion, WADA -- which is supposed to police decisions by national authorities -- allowed it to stand, a position that has led to an uproar in global athletics since it was disclosed by The Times and the German broadcaster ARD in April.
The data from China's human trials shows only how the body processes the drug over time, the doctors and scientists who reviewed it for The Times said, and does not show whether the levels that were in the swimmers' systems could have been caused by intentional doping or accidental contamination.
"In my opinion, the scientific data cannot distinguish between" contamination or doping, said David Cowan, a professor emeritus at King's College London and a leading antidoping scientist who was in charge of the testing laboratory at the London 2012 Olympics.
Informed by The Times of the conclusion reached by the outside experts, WADA said that it "fully stands by" its handling of the case. The organization reiterated its position that it did not have sufficient evidence to challenge China's conclusions and win any further legal battle over the episode, and that its conclusions were shared by World Aquatics, the governing body for international swimming.
"Despite the close scrutiny of our scientific and legal experts, it was clear on the evidence that we could not challenge the contamination scenario," WADA said in a statement. "The science, the applicable rules and ultimately the advice from external legal counsel confirmed that if we appealed the cases to the Court of Arbitration for Sport, we would lose."
Throughout the last year, WADA and officials in the Olympic movement have cited China's science in defending their handling of the cases.
In a letter to Congress in June, a lawyer for WADA said that as the agency weighed disciplinary action after the swimmers tested positive, it requested the Chinese officials' entire case file on the positives.
"WADA ultimately determined that contamination was compatible with the analytical data in the file and that it had no basis to challenge that contamination was the source of TMZ," Robert Kelner, a lawyer for WADA, told Congress in June.
But the questions raised by what outside experts told The Times are stoking further concerns among members of Congress who have been pressing for more transparency and accountability from WADA.
"WADA has stonewalled and tried to intimidate advocates for fair play at every single turn, so it is unsurprising that its officials would also lie to Congress," said Senator Marsha Blackburn, Republican of Tennessee.
She called for withholding congressional funding to the group if it could not show it was operating as "a fair and independent actor." The United States contributes more to WADA's budget than any other country.
For China, proving contamination in the swimming case was extremely important, antidoping experts said, because it was one of the few explanations that would allow the athletes to avoid suspension before that summer's Olympics.
As part of the human studies, some volunteers were given a normal therapeutic dose of TMZ and others were provided with minuscule amounts, similar to what they might ingest through contamination.
Experts in antidoping research said that while it was not uncommon to conduct human trials after an athlete tested positive, the number of participants the Chinese were able to recruit, in such a short period of time, stood out, particularly because the trial took place during the coronavirus pandemic.
The research showed that even at the therapeutic dose, the amount of the drug in the volunteers' systems could drop to the very low levels the swimmers tested positive for after as little as 11 days.
That period of time is significant.
The Chinese swimmers had been repeatedly tested earlier in 2020. But in the month before the meet, the testing dropped off. According to Chinese documents, six athletes were tested in the month before the meet, but the test that occurred closest to the competition came 12 days before it started.
When the human experiments were concluded, the Chinese made two central claims that they said proved contamination.
The primary claim focused on how the low concentration of the drug in the samples was compatible with contamination, not doping. The Chinese said that the level of the drug was so low that it could provide no performance-enhancing benefit at the time of competition. They did not address the possibility that the swimmers had taken the drug to enhance their training.
"Focusing on just one aspect to prove a point is known as cognitive bias," Dr. Cowan said.
The Chinese, Dr. Cowan said, did not appear to have fully considered that the positive tests could just have likely been the tail end of a full dose 11 or more days after taking the drug.
The second claim focused on how the swimmers tested positive. Over the three-day meet, many of the athletes were tested several times, and some of them alternated between negative and positive results. That pattern, the Chinese said, was indicative of contamination, not doping, an assertion later echoed by WADA.
But the scientists who examined the data said that explanation was overly simplistic. As a drug passes through the body, they said, low levels of it can be picked up one day and missed the next, depending on how much water is in someone's system and how the body processes the drug.
WADA's own top scientist had trouble believing the contamination story, according to an investigation it commissioned. But without being able to disprove the theory, the WADA scientist felt compelled to accept it even if he continued to have doubts about the Chinese claims, the report said.
An unidentified scientific expert who was quoted in the same report said the science was far more equivocal than the Chinese and WADA made it out to be, and said doping could not be ruled out.
But the lack of conclusiveness from the science did not stop the Chinese or WADA from pushing the contamination claim.
"The reality is that there is not a single piece of evidence to challenge the environmental contamination theory," WADA's president, Witold Banka, told an agency board in May. "All the scientific evidence points to contamination."