Death after interrogation
Passaro, a former Special Forces medic, was convicted last August of beating Abdul Wali, who died of his injuries two days after a June 2003 interrogation.
Prosecutors said Passaro beat the prisoner so badly that he pleaded to be shot to end his pain.
The indictment said Passaro worked at a US military base in Afghanistan that was frequently subjected to rocket attacks and Wali was a suspect in the attacks.
Passaro's lawyers portrayed their client as someone who went out of his way to offer care to Wali.
They said Passaro even performed mouth-to-mouth resuscitation in an unsuccessful bid to revive him.
Guidelines broken
Guidelines given to interrogators have been an issue since a scandal broke over the abuse and humiliation of prisoners by Americans at Iraq's Abu Ghraib prison in 2004.
Prisoners released from the US naval base at Guantanamo Bay in Cuba, where the United States is holding suspected Taliban and al-Qaeda members, also say they were tortured or abused.
Critics say US government guidelines on what constitutes torture, issued since the September 11 attacks, have created a climate in which abuses of detainees have flourished.