WASHINGTON - The US urged military interrogators at the notorious Guantanamo Bay prison to destroy their handwritten notes to minimize evidence in case they were called to testify in court about potentially cruel treatment of detainees, a military defence lawyer said Sunday. The standard operating procedure for interrogators says: "Keeping the number of documents with interrogations information to a minimum can minimize certain legal issues." The lawyer for Toronto-born Omar Khadr, Lieutenant Commander William Kuebler, said the instructions included in the operations manual that were shown to him by prosecutors suggested Pentagon deliberately thwarted evidence that could help terror suspects defend themselves at trial. Kuebler said the apparent destruction of evidence prevents him from challenging the reliability of any alleged confessions. He said he plans to file the document with the US Supreme Court - which is expected to rule this month on whether prisoners should be able to appeal their detention to a regular US court - to seek a dismissal of charges against Khadr. However, prosecutors claim no such notes exist for early interrogations of Khadr, who faces life in prison for allegedly throwing a grenade that killed a US soldier in a 2003 firefight in Afghanistan, Kuebler said. Destroying evidence is an apparent violation of federal and military law. A Pentagon spokesman, Jeffrey Gordon, said he was reviewing the matter Sunday evening. Khadr, now 21, was born in Toronto. His family moved to Peshawar when he was four. He was arrested in Afghanistan in 2002 by the U.S. military. They declared him an enemy combatant and shipped him to Guantanamo Bay.