California ? A former Marine accused of killing unarmed Iraqi detainees was acquitted of voluntary manslaughter Thursday in a first-of-its-kind federal trial that ended with some of the jurors shaking hands and hugging the defendant and his sobbing mother.

The jury in Riverside took less than 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, during some of the fiercest fighting of the war.

The verdict left the 28-year-old defendant – and some of the jurors – in tears.

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.

Prosecutors alleged that Nazario either killed or caused others to kill four unarmed Iraqi detainees in Fallujah during “Operation Phantom Fury,” which resulted in house-to-house fighting.

Other former Marines testified during the five-day trial that they did not see Nazario kill detainees but heard the gunshots.

The case came to light in 2006 when Sgt. Ryan Weemer, Nazario’s former squadmate, volunteered details to a U.S. Secret Service job interviewer during a lie-detector screening that included a question about the most serious crime he ever committed. That screening was not admitted at Nazario’s trial.