A former Blackwater security guard has been sentenced to life in prison and three others to 30 year jail terms over the killing of 14 Iraqi civilians in 2007.
In addition to the killings 17 others were injured.
The sentencing closes a case which had outraged Iraqis and inflamed anti-US sentiment around the world.
The shootings also sparked a debate over the role of defence contractors in warfare.
Nick Slatten (31) from Tennessee was convicted last year of murder for killing the driver of a car, the defendants had argued at trial they believed contained a bomb.
Paul Slough (35), from Texas, Evan Liberty (32)from New Hampshire and Dustin Heard (33) also from Tennessee were all convicted of multiple counts of manslaughter and attempted manslaughter.
In their statements afterwards, all four former guards maintained their innocence. and their lawyers said they would be launching appeals.
On September 16, 2007 the four guards had opened fire with machine guns and grenade launchers on the Iraqis including women and children in Baghdad’s crowded Nisur Square.
Although the incident strained relations between the US and the Iraqi government, things have since improved resulting in today’s visit by Iraq’s Prime Minister Haider al-Abadi to the White House.