A former Blackwater guard was just sentenced to life in prison for a 2007 shooting in Baghdad

WASHINGTON (Reuters) - US District Court Judge Royce Lamberth sentenced former Blackwater security guard Nicholas Slatten to life in prison for murder in connection with the 2007 massacre of 14 unarmed Iraqis, closing a chapter of the US war in Iraq that tested relations between the two countries.

Slatten had been convicted by a jury in October.

Three other guards had been found guilty of manslaughter, but Slatten was the only one convicted of first-degree murder.

The guards had been in the employ of the US State Department, and had "fired heavy machine guns and grenade launchers from their armored convoy in the mistaken belief they were under attack by insurgents" in Baghdad's Nisour Square according to the Guardian. Slatten is believed to have been the first to open fire.

The incident drew attention to the role of private security contractors in Iraq and tarnished Blackwater's reputation. But the company was sold in 2010 and re-named Academi, and one of its subsidiaries signed $92 million in security contracts with the US State Department in 2013.