Two marines refused to testify against Mr Nazario
In a landmark trial, a US federal jury has cleared a former marine sergeant of the deaths of Iraqi detainees.
The trial of Jose Luis Nazario is the first time a civilian jury has decided on the alleged crimes of a former US soldier while he was on active duty.
Mr Nazario, 28, was charged with voluntary manslaughter and assault over the deaths of four unarmed Iraqis in 2004 during the battle for Falluja.
The California trial used a law passed to prosecute civilian contractors.
Several marines had alleged that Mr Nazario shot dead two Iraqi men who had been detained while his squad searched a house in the city of Falluja.
He is alleged to have ordered two other marines to shoot two other unarmed prisoners.
But the prosecution's case fell apart when two marines refused to testify. Marines Jermaine Nelson and Ryan Weemer were found in contempt of court.
The jury took six hours to decide that Mr Nazario was not guilty.
His lawyer, Kevin McDermott, had told the jury that they could not convict Mr Nazario for an alleged crime in which there were no bodies, no identities for the alleged victims and no forensic evidence of any deaths.
Mr Nazario, who left the US Marine Corps in 2006, had faced up to 10 years in jail if found guilty of all the charges against him.
Two active service marines allegedly involved in the same incident face courts martial later this year.