Four Blackwater operatives have been sentenced to lengthy prison terms for their role in the 2007 massacre of unarmed civilians at Baghdad’s Nisoor Square. A jury handed down guilty verdicts last year over the killings of 14 of the 17 Iraqis who died when the defendants’ Blackwater unit opened fire. On Monday, Nicholas Slatten was sentenced to life in prison for first-degree murder, while three other guards convicted of manslaughter were sentenced to 30 years each. In their first public statements on the killings, each of the operatives professed their innocence to the sentencing judge. The trial, and Monday’s hearing, featured testimony from witnesses who survived the attack and saw loved ones gunned down. Nisoor Square is the highest-profile deadly incident involving Blackwater or any private war contractor. The case lagged for years with prosecutors accused of dragging their feet and a lower court’s dismissal of the charges in 2009. In response to the sentences, Jeremy Scahill, author of “Blackwater: the Rise of the World’s Most Powerful Mercenary Army,” said: “People who gun down innocent Iraqis … must answer for their crimes. So too should those who sent them there to kill at will.”