WASHINGTON - Four security guards belonging to the notorious Blackwater Worldwide firm were convicted in Washington Wednesday on charges stemming from a deadly 2007 shooting in Iraq that resulted in the death of 14 civilians.

 The verdict reinforced assertions that gunfire in Baghdad’s crowded Nisour Square seven years ago was deliberate. The shooting exacerbated global anti-American sentiment and gave credibility to accusations that the security firm - part of the U.S. State Department’s security in Iraq — was without control or accountability.

The four responded to a car bomb explosion on Sept. 16, 2007 and, prosecutors said, fired at Iraqis although unprovoked. The defendants maintained in court they justifiably shot in self-defence.

After an 11-week trial, Nicholas Slatten was found guilty of murder, and Dustin Heard, Evan Liberty and Paul Slough were found guilty on manslaughter, attempted manslaughter and gun charges. They claimed in federal court they were ambushed, and that the civilian casualties were the unintended consequences of war.

The jury’s verdict marked an end to a years-long quest by prosecutors to bring the case to trial, and experts called it a milestone in the government’s efforts to monitor security contractors’ conduct on the battlefield.

The contractor shootings and the American government’s refusal to allow the men to be tried in Iraq sent relations between the two countries into a crisis, and the Blackwater name became shorthand for unaccountable US power.

In Congress, lawmakers denounced the Nisour Square shooting as recently as July, but legislation that would provide clearer jurisdiction for U.S. prosecutors and investigators to pursue criminal wrongdoing overseas by private security contractors has languished for years.

The security firm’s founder, Erik Prince, eventually left the company, which was renamed Xe Services and then Academi.

The defendants were among 19 Blackwater Worldwide guards providing security for State Department officials in Iraq. At the time of the incident, their convoy was clearing the way for another Blackwater team evacuating a U.S. official from a nearby car bombing. David Schertler, who represents one of the guards, Dustin Heard, called the verdict “incomprehensible.” “The verdict is wrong,” he said. “We’re devastated. We’re going to fight this every step of the way,” he said.