A federal appeals court said Wednesday that John Yoo, the George W. Bush administration lawyer who wrote memos used to rationalize torture of suspected terrorists, cannot be sued by enemy combatants who claim they were tortured.

Yoo, who was the deputy assistant attorney general in the Justice Department's Office of Legal Counsel from 2001 to 2003, was sued by Jose Padilla, the so-called "dirty bomber." Padilla, an American citizen, claims Yoo's internal legal opinions paved the way for his harsh interrogation while he was secretly held without charges at a Navy brig in South Carolina for more than three years.

A federal judge said in 2009 that Padilla, who was convicted of terror-related charges, could sue Yoo for damages because his lawsuit "has alleged sufficient facts to satisfy the requirement that Yoo set in motion a series of events that resulted in the deprivation of Padilla's constitutional rights." Yoo's memos concluded that techniques such as prolonged sleep deprivation, binding in stress positions, and waterboarding did not amount to torture.

Hearing Yoo's appeal, a three-judge panel of the 9th U.S. Circuit Court of Appeals agreed with Yoo's contention that he should be immune from the suit because it was not clearly established that harsh treatment was unconstitutional. Padilla claims he "suffered gross physical and psychological abuse" by government authorities, which included death threats, psychotropic drugs, shackling and manacling, and being subjected to noxious fumes and constant surveillance.

"It was not 'beyond debate' at that time that Padilla – who was not a convicted prisoner or criminal defendant, but a suspected terrorist designated an enemy combatant and confined to military detention by order of the president – was entitled to the same constitutional protections as an ordinary convicted prisoner or accused criminal," Judge Raymond Fisher wrote for the 3-0 appeals court.

Fisher added that, even today, "it remains murky whether an enemy combatant detainee may be subjected to conditions of confinement and methods of interrogation that would be unconstitutional if applied in the ordinary prison and criminal settings."

Yoo, now a University of California, Berkeley law professor, said in an e-mail that Padilla now "will need to find a new hobby for his remaining time in prison."

The appellate court's decision, he said, "confirms that this litigation has been baseless from the outset. For several years, Padilla and his attorneys have been harassing the government officials he believes to have been responsible for his detention and ultimately conviction as a terrorist."

Padilla, of Brooklyn, was charged originally in connection to an al-Qaeda plot to unleash a radioactive "dirty bomb" in the United States. Padilla is serving a 17-year sentence after being convicted of unrelated charges of conspiring to commit murder overseas.