WASHINGTON (AP) — A federal judge has sentenced a former Blackwater security contractor to life in prison for his role in the 2007 shooting of unarmed civilians in Iraq.

Judge Royce Lamberth issued the sentence Wednesday after friends and relatives requested leniency for Nicholas Slatten, who was found guilty of first-degree murder by a jury in December.

Prosecutors charged that Slatten was the first to fire shots in the September 2007 massacre of Iraqi civilians at a crowded traffic circle in Baghdad. In all, 10 men, two women and two boys, ages 9 and 11, were killed.

The defense had argued that Slatten and other Blackwater contractors opened fire only after they saw what they mistakenly thought was a potential suicide car bomber moving quickly toward their convoy.