The United States has dropped charges against a Saudi man that had been considered “the 20^th hijacker” in the September 11, 2001, terrorist attacks.

Mohammed al-Qahtani was one of the six Guantanamo Bay inmates who had been charged with murder and war crimes in February. All the other five men face the death penalty if convicted. Charges against them were approved Friday.

Susan Crawford, the convening authority for military commissions, refused to approve prosecutors’ charges against Al-Qahtani, but the reasons for her decisions have not yet been revealed. Crawford dismissed the charges against Al-Qahtani without prejudice, meaning they can be filed again later.

Mohammed admitted he had planned every aspect of the September 11 attacks, but his confession cannot be taken into account as evidence, because the CIA acknowledged it used torturing interrogation techniques on him, including “waterboarding,” a technique that simulates drowning and that has been widely criticized as a method.

According to the Associated Press, Al-Qahtani said he was beaten, threatened with dogs, exposed to loud music and freezing temperatures, as well as stripped nude in front of female police officers.

The U.S. alleged that Al-Qahtani missed becoming the 20^th hijacker on September 11, as he was denied entry into the country by immigration agents at the airport in Orlando, Florida. He had more than US$2,400 with him in cash when he was stopped by the agents, and didn’t have any return ticket.

The September 11 attacks killed nearly 3,000 people after hijacked jetliners crashed into the World Trade Center in New York, the Pentagon and a field in Pennsylvania.