Ahmed Mohammed Ahmed Haza al-Darbi was transferred to Saudi Arabia from the detention center, bringing the number of detainees remaining at Guantanamo Bay to 40, the Department of Defense said.
"In a February 2014 plea, al-Darbi pled guilty at a military commission. Now, having complied with the terms of that agreement, al-Darbi will serve out the balance of his 13-year sentence in Saudi Arabia. He has waived his right to appeal," the Pentagon said.
Al-Darbi pleaded guilty to charges related to helping plot a 2002 al-Qaida attack on a French oil tanker. As part of the plea agreement he was ordered to testify against two other Guantanamo detainees in exchange for being allowed to serve the remainder of his 13-year sentence in Saudi Arabia.
The Pentagon said the secretary of defense notified Congress of the transfer in accordance with statutory requirements.
"The United States coordinated with the government of the Kingdom of Saudi Arabia to ensure the transfer took place in accordance with established standards for security and humane treatment," the Pentagon said.
Al-Darbi issued a statement to The New York Times through his volunteer lawyer, Ramzi Kassem, condemning the practice of sending prisoners to Guantanamo Bay without a trial.
"My words will not do justice to what I lived through in these years and to the men I leave behind in prison," he said. "No one should remain at Guantanamo without a trial. There is no justice in that."
Earlier Wednesday U.S. Defense Secretary Jim Mattis issued guidelines stating the United States will continue to send suspected terrorists to Guantanamo Bay if they pose a "continuing, significant threat" to the country.
"The secretary of defense has provided the White House with an updated policy governing the criteria for transfer of individuals to the detention facility at U.S. Naval Station Guantanamo Bay," Defense Department spokeswoman Cmdr. Sarah Higgins said. "This policy provides our warfighters guidance on nominating detainees for transfer to Guantanamo detention should that person present a continuing, significant threat to the security of the United States."