Sun said he was aware that the DCO was from IDTM because "I made a complaint about the DCO in 2017 when the tester failed to show an authorized document."

Chinese anti-doping expert Han Zhaoqi said that athletes will not refuse to take doping tests if the DCOs have proper credentials.

"Athletes will not refuse to take doping tests as long as they can confirm that the DCOs are authorized and have proper credentials," said Han, a doctor and professor from Zhejiang College of Sports, in the hearing.

"I can't call the vials of blood they took 'doping test samples' because they were taken by people who were not properly credentialed and authorized," said Han.

"I take anti-doping lectures every year at China Anti-Doping Agency (CHINADA). And I know that CHINADA issues DCO credential to each and every DCO in China, and they also repeatedly stress that athletes should make sure they see the credential and confirm DCOs' identifications," he said.

"What China does is to truly uphold WADA's World Anti-Doping Code," he added.

Sun, the first Chinese man to win an Olympic swimming gold, said in his testimony that he was familiar with CHINADA's high level of doping control process.

"China's doping control has a really high standard. I take training in this area and they (Chinese DCOs) will show me their credentials," said Sun during a hearing which was marred by poor translations.

Before the hearing started, Sun told Xinhua that he intended for all who are following the case to know the truth.

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