The World Anti-Doping Agency on Tuesday defended the "strong reputation" of its choice of veteran Swiss prosecutor Eric Cottier to review how it handled the case of positive doping tests by 23 Chinese swimmers.

Cottier is "entirely independent" of WADA and international sports, it said, even as scrutiny of him increased over his friendship with a longtime colleague who worked with the agency and his enquiries into German broadcaster ARD's previous investigation of a separate Olympic sport.

Cottier has been given until a few weeks before the start of the Paris Olympics in July to report on WADA's acceptance in 2021 — in the months before the Tokyo Olympics and 2022 Beijing Winter Games held in a public health lockdown — of Chinese authorities' explanation that the swimmers were contaminated by a banned heart medication found in a hotel kitchen.

The positive tests, including for three Chinese swimmers who won gold medals in Tokyo, were eventually detailed April 20 after months-long investigations by ARD and the New York Times.

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Montreal-based WADA has since faced widespread skepticism from anti-doping officials, national swim teams and athlete groups about its decisions three years ago and picking Cottier.

For 17 years through 2022, Cottier was the attorney general of Vaud, the home canton (state) of the International Olympic Committee where WADA has its European office in Lausanne.

Choosing a prosecutor on the doorstep of the Olympic movement was "highly problematic," Swiss anti-corruption expert Mark Pieth told The Associated Press on Monday.

During the last 13 years that Cottier was chief public prosecutor, the Vaud police commander was Jacques Antenen, who also worked with WADA from 2018 until last December as supervising auditor of the doping watchdog's investigations team.

"I think it's highly problematic and it's totally unnecessary," Pieth said of WADA's selection process. "It shows they don't have the awareness of possible conflicts of interest."

When Antenen retired from Vaud police in 2022, the service's in-house magazine published a photograph from the ceremony of him with Cottier captioned as the prosecutor having come "to greet an old friend."

"The fact that he [Antenen] might know Mr. Cottier professionally in no way compromises Mr. Cottier's independence in reviewing WADA's handling of this case," the agency said in a statement. It did not address a question asking if Antenen took part in nominating the special prosecutor.

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Pieth was contacted by Cottier after speaking with ARD in 2020 for its investigative reporting of financial corruption and cover-ups of doping cases at the International Weightlifting Federation, which had an office in Lausanne.

Though the Vaud prosecution office then led by Cottier inquired about the issues in weightlifting raised by ARD in January 2020, it is unclear if further steps were taken.

The office did not immediately respond to questions sent by email on Tuesday.

Antenen produced annual reports over six years on his oversight and advisory work with the WADA investigations team, which was involved in the Chinese swimming case.

In his 2021 audit, Antenen said the WADA unit "alone cannot bear all of the responsibility for anti-doping investigations," and called for it to verify the skills of national anti-doping bodies like China's "to promote the creation of effective, independent and honest structures."

WADA has insisted since the ARD and New York Times reports that its legal, scientific and investigations managers agreed that evidence presented by China was consistent with the contamination theory and that all due process was followed.