Monday, the United Nations Special Rapporteur on Torture Manfred Nowak told CNN's Rick Sanchez that the US has an "obligation" to investigate whether Bush administration officials ordered torture, adding that he believes that there is already enough evidence to prosecute former Secretary of Defense Donald Rumsfeld.

"We have clear evidence," he said. "In our report that we sent to the United Nations, we made it clear that former Defense Secretary Donald Rumsfeld clearly authorized torture methods and he was told at that time by Alberto Mora, the legal council of the Navy, 'Mr. Secretary, what you are actual ordering here amounts to torture.' So, there we have the clear evidence that Mr. Rumsfeld knew what he was doing but, nevertheless, he ordered torture."

Asked during an interview with Germany's ZDF television on Jan. 20, Nowak said: "I think the evidence is on the table."

At issue, however, is whether "American law will recognize these forms of torture."

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A bipartisan Senate report released last month found Rumsfeld and other top administration officials responsible for abuse of Guantanamo detainees in US custody.

It said Rumsfeld authorized harsh interrogation techniques on December 2, 2002 at the Guantanamo prison, although he ruled them out a month later.

The coercive measures were based on a document signed by Bush in February, 2002.

This video is from CNN's Newsroom, broadcast Jan. 26, 2009.