A former Marine accused of killing unarmed Iraqi detainees has been acquitted of voluntary manslaughter in a first-of-its-kind federal trial.

The jury took six hours to find Jose Luis Nazario Jr. not guilty of charges that he killed or caused others to kill four unarmed detainees on Nov. 9, 2004, in Fallujah, Iraq.

Thursday’s verdict marks the first time a civilian jury has determined whether the alleged actions of a former military service member in combat violated the law of war.