Among the positive developments cited by Mr. Wu in his address to the panel were the abolition of re-education through labor in December 2013 and a reduction in the number of offenses punishable by the death penalty.

Amendments to the criminal procedure law have strengthened the exclusion of “illegally obtained evidence,” including evidence extracted by torture, he said. In 2014, he said, the authorities decided not to approve the arrests of 406 people and not to prosecute 106 others because the evidence against them had been obtained illegally.

But the committee cited a Human Rights Watch analysis of 432 verdicts since the start of 2014 in court cases where suspects said they were tortured. Only 23 resulted in evidence’s being thrown out of court and none resulted in the prisoner’s acquittal, the panel noted. What measures were taken against those who extracted the confession? the panel asked.

Mr. Wu also said that judicial authorities and prison workers were receiving anti-torture training and that the rights of lawyers were being strengthened. “Lawyers are an indispensable part in China’s rule of law,” he said. “A key component of our plan to comprehensively advance law-based governance is to strengthen and protect lawyers’ rights to practice law.”

Members of the panel were not convinced. In questions presented over more than two hours, they pressed for details about the number of lawyers now in detention and what the charges were; the number of black, or unofficial, places of detention that exist; the number of prisoners held in those places and who controlled them; what access prisoners had to medical care; the number of cases of torture authorities had recorded; and the number of torture cases involving Tibetan prisoners.

Felice D. Gaer, the committee’s vice chairwoman, said the panel had learned that the Chinese authorities had threatened seven Chinese people who wanted to provide information to the panel, and had detained some who defied those warnings on the grounds that their trip might endanger national security. Did the Chinese authorities think that working with the committee and cooperating with United Nations human rights mechanisms constituted a threat to national security? she asked.