A former Blackwater security guard has been sentenced to life in prison and three others to 30-year terms over the killing of 14 Iraqi civilians in 2007.
U.S. District Judge Royce Lamberth announced the sentences on April 13 following a daylong hearing in a Washington court.
Nicholas Slatten, who witnesses said was the first to fire shots in the incident, was sentenced to life on a charge of first-degree murder.
Paul Slough, Evan Liberty, and Dustin Heard were each sentenced to 30 years in prison for charges that included manslaughter, attempted manslaughter, and using firearms while committing a felony.
The four men were convicted in October 2014 for the carnage in Baghdad's crowded Nisoor Square.
Seventeen people were also wounded when the private contractors opened fire to clear the way for a U.S. convoy.
The incident sparked an international uproar over the use of private security guards in a war zone.
During the April 13 hearing, defense lawyers argued for leniency, reaffirming that the former guards were targeted with gunfire and shot back in self-defense.
Prosecutors described the shooting as an unprovoked ambush against civilians and argued that the sentences be made even harsher because the former guards had never expressed any remorse.
"These four men have refused to accept virtually any responsibility for their crimes and the blood they shed that day," Assistant U.S. Attorney Patrick Martin said.
But Lamberth rejected both requests, telling the court, "Based on the seriousness of the crimes, I find the penalty is not excessive."
Victims and witness were flown from Iraq to the United States for the trial.
Mohammad Kinani Al-Razzaq, whose nine-year-old son was killed in the attack, told the court, “What's the difference between these criminals and terrorists?''
With reporting by Reuters, AP, and the BBC