Michael Behenna was convicted of unpremeditated murder and sentenced to 25 years in a military prison.
An Army first lieutenant, Behenna was serving as a platoon leader in Iraq in 2008 when an insurgent attack with an improvised explosive device ripped through his patrol, killing two soldiers and three Iraqi civilians.
Later, Behenna interrogated a suspected insurgent linked to the deadly attack by intelligence reports that identified the suspect as a member of the local "al-Qaida in Iraq IED [improved explosive device] cell."
Alone with his prisoner in the desert except for his translator, Behenna pulled his pistol and shot him twice, killing him. He later said the prisoner made a move to grab the pistol, a fact disputed by the translator.
A bare majority of the Court of Appeals for the Armed Forces ruled that Behenna "lost the right to act in self-defense as a matter of law" because it was an unauthorized interrogation and he had drawn his pistol.
"Even assuming that a service member becomes an initial aggressor by pointing a firearm at a suspected enemy without authorization," Behenna's petition to the Supreme Court said, "the common law of self-defense does not categorically equate gun pointing with 'deadly force' that wholly forfeits the defender's right to repel a lethal attack."
The military appeals court's decision "is not only wrong, but dangerous," the petition said. "It puts service members in combat zones in a more vulnerable position than their civilian law enforcement counterparts."
The U.S. Supreme Court rejected review without comment.