A UN watchdog has found the US and seven other nations liable for the torture and wrongful imprisonment of a Saudi Arabian prisoner awaiting a death sentence trial at the Guantanamo Bay detention facility.

The United Nations Working Group on Arbitrary Detention detailed that imprisonment at Guantanamo following the US alleged "war on terror" could be equivalent to crimes against humanity. 

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The lawsuit was launched by Abd Al-Rahim Al-Nashiri, a Saudi national of Yemeni ancestry suspected of orchestrating the suicide bombing of the USS Cole missile destroyer in October 2000, which killed 17 Americans.

In the evidence presented to the working committee last June, attorneys said after Al-Nashiri was apprehended in Dubai in 2002, he was subjected to 4 years of torture and mistreatment at numerous CIA black sites in Afghanistan, Lithuania, Morocco, Poland, Romania, and Thailand.

He landed in Guantanamo Bay in 2006 and is still held there.

Accused in 2008, his death penalty case is still pending. 

The UN working committee, a group comprised of five independent experts whose judgments are not legally enforceable but have significant reputational weight, found that all eight nations were "jointly responsible for the torture and cruel, inhuman, and degrading treatment of Mr. Al-Nashiri" in an opinion issued last year and announced Friday. 

The committee also expanded on how the countries were responsible for his "arrest, rendition, and arbitrary detention,"  adding that submissions of his torture "stand unrefuted".

According to Sylvain Savolaine, Al-Nashiri's lawyer, the decision is of immense importance. 

The group urged the nations to remedy the situation of Al-Nashiri "without delay" and stated that they believe the appropriate course of action would be his immediate release along with compensation and reparations. 

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Additionally, the group encouraged "a full and independent investigation of the circumstances surrounding the arbitrary deprivation of liberty of Mr. al-Nashiri, including an independent inquiry into his allegations of torture."

The specialists were particularly concerned about the situation in Guantanamo, which presently houses 31 detainees. They stated, among other things, that the medical treatment provided there "has been and remains grossly deficient."

"The Working Group is obliged to remind the government of the United States that all persons deprived of their liberty must be treated with humanity and with respect for the inherent dignity of the human person," they expressed.

The group also added that other prisoners in Guantanamo may have the same conditions applied to them, warning that "widespread or systematic imprisonment or other severe deprivation of liberty, in violation of international law, may constitute crimes against humanity."