Updated

A federal appeals court Friday overturned a former Blackwater security contractor's first-degree murder conviction in connection with a 2007 shooting in Baghdad that killed 14 Iraqi civilians and injured 17 others.

In a split decision, the three-judge panel of the U.S. Court of Appeals of the District of Columbia Circuit ruled a lower court erred by not allowing Nicholas Slatten to be tried separately from his three co-defendants in 2014.

Slatten, 33, had been sentenced to life in prison for his role in the shooting, in which prosecutors claimed he had fired the first shots.

The court also ordered new sentences for the three other contractors — Paul Slough, Evan Liberty and Dustin Herd — who were each found guilty of manslaughter and firearms charges carrying mandatory 30-year terms.

The judges determined those sentences were "grossly disproportionate to their culpability for using government-issued weapons in a war-zone." Prosecutors had charged the men with using military firearms while committing another felony. That statute, typically employed against gang members or bank robbers, had never before been used against overseas security contractors working for the U.S. government.

It was not immediately clear whether prosecutors planned to try Slatten again for murder.

"The U.S. Attorney’s Office is reviewing the opinion and has no further comment at this time," spokesman William Miller told Fox News

At the weekslong trial three years ago, federal prosecutors and defense lawyers presented very different versions of what triggered the September 2007 massacre in Nisour Square.

The government described the killings as a one-sided ambush of unarmed civilians, while the defense said the guards opened fire only after a white Kia sedan seen as a potential suicide car bomb began moving quickly toward their convoy. After the shooting stopped, no evidence of a bomb was found.

In issuing their ruling benefiting the defendants, the judges said they were in no way excusing the horror of events they said "defies civilized description."

"In reaching this conclusion, we by no means intend to minimize the carnage attributable to Slough, Heard and Liberty's actions," said U.S. Circuit Judge Karen L. Henderson, writing for the court. "Their poor judgments resulted in the deaths of many innocent people."

Fox News' Jake Gibson and the Associated Press contributed to this report.