Relatives of an Oklahoma soldier convicted of killing an unarmed Iraqi prison detainee said they're surprised a military appeals court upheld his conviction.

Scott and Vicki Behenna told reporters after the court's decision this week that they will pursue whatever legal action they can to bring their son, 1st Lt. Michael Behenna, home.

Their comments come after a military appeals court on Thursday narrowly rejected Behenna's request to overturn his 2009 conviction for unpremeditated murder in a combat zone. Behenna, who is from Edmond, Okla., is serving a 15-year sentence at a military prison in Fort Leavenworth, Kan.

Prosecutors said Behenna shot the detainee, Ali Monsour Mohammed, execution-style after interrogating him at gunpoint about a 2008 roadside bombing that killed two men under Behenna's command.

Behenna's father said he is confident his son was acting in self-defense.

"Although he may have made some mistakes, he is in prison not for executing someone as was alleged and prosecuted," Scott Behenna said, according to The Oklahoman (http://bit.ly/Ne0mcv).

Behenna's lawyer, Jack Zimmerman, argued that the military trial judge gave jurors faulty instructions that took away Behenna's claim of self-defense.

Although the U.S. Court of Appeals for the Armed Forces agreed that the judge's instructions were flawed, it determined the error was "harmless" and did not affect the verdict or the sentence.

Vicki Behenna, herself a veteran federal prosecutor, said her son's spirits remain high despite with court's ruling.

"He doesn't belong in prison," Michael Behenna's brother Brett said. "What happened (Thursday) was a complete surprise."

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Information from: The Oklahoman, http://www.newsok.com