U.N. Commission Presses U.S. on Torture WASHINGTON - A United Nations panel that monitors compliance with an antitorture treaty expressed skepticism Thursday about American law enforcement and national security practices. In a two-day presentation in Geneva, the American delegation acknowledged that the United States had tortured terrorism suspects after the Sept. 11 attacks. It emphasized, however, that the government had since tightened its rules, including with a 2005 statute against using cruelty and a 2009 executive order by President Obama that limits interrogators to a list of techniques in an Army field manual. Alessio Bruni of Italy, a member of the United Nations committee, pressed the delegation to explain Appendix M of the manual, which contains special procedures for separating captives in order to prevent them from communicating. The appendix says that prisoners shall receive at least four hours of sleep a day - an amount Mr. Bruni said would be sleep deprivation over prolonged periods and unrelated to preventing communication. Brig. Gen. Richard C. Gross, the top legal adviser to the Joint Chiefs of Staff, said that reading the appendix as intended to permit sleep deprivation was a misinterpretation. Four hours is "a minimum standard; it's not the maximum they can get," he said, adding that the rule had to be read in the context of the rest of the manual, including a requirement for medical and legal monitoring of treatment "to ensure it is humane, legal and so forth." Mr. Bruni was not persuaded. He said that calling the provision a minimum standard still meant four hours a night for long periods was "permissible." He suggested that Appendix M "be simply deleted." In the presentation, streamed live online from Geneva, the committee also scrutinized whether the United States had adequately investigated the C.I.A."s Bush-era "rendition, detention and interrogation" program for high-level suspects linked to Al Qaeda. A provision of the treaty, the Convention Against Torture, requires parties to investigate and provide accountability for past instances of torture. The American delegation said that the United States had investigated the C.I.A. program, and that the coming publication of a Senate Intelligence Committee report would add to the public record. "Our goal is to move forward, but we know that to avoid falling backward, we must be willing to look backward and to come to terms with what happened in the past," said Tom Malinowski, the assistant secretary of state for human rights. Mr. Malinowski's remark was a twist on a comment Mr. Obama made in January 2009, that when it came to previous C.I.A. practices, "we need to look forward as opposed to looking backwards." The American officials pointed to a criminal investigation by John H. Durham, an assistant United States attorney in Connecticut, whom Michael B. Mukasey, then attorney general, appointed in 2008 to look at whether the C.I.A. had broken the law by destroying videotapes of its interrogations of Qaeda suspects. In 2009, Attorney General Eric H. Holder Jr. expanded Mr. Durham's mandate to look at C.I.A. torture that went beyond what the Justice Department had said was legal. Mr. Durham eventually closed the investigation without indicting anyone. Another member of the United Nations panel, Jens Modvig of Denmark, pressed for details. He asked if Mr. Durham's team had interviewed any current or former detainees. David Bitkower, a deputy assistant attorney general in the Justice Department's criminal division, said that the team had interviewed about 96 witnesses, but that he could not identify them because no charges had been filed. He rejected Mr. Modvig's suggestion that the investigation had not been vigorous. "Not only was there not an attempt to not find the truth, there was an attempt to re-evaluate previous decisions that were made to make sure we got it right this time," Mr. Bitkower said. Laura Pitter of Human Rights Watch called the Obama administration's refusal to say whether it had interviewed detainees as witnesses "unacceptable." She cited a 2012 investigation by her group into the cases of several Libyans who said the C.I.A. had tortured them, saying Mr. Durham's team had never interviewed them. "We know absolutely that key witnesses," like those subjected to torture "that went beyond what was authorized in C.I.A. custody, were not interviewed," Ms. Pitter wrote in an email.