WASHINGTON — A former Blackwater Worldwide contractor accused of firing the first rounds in a mass shooting that killed more than a dozen unarmed civilians in a Baghdad traffic circle in 2007 was found guilty of one count of murder Wednesday.

Nicholas Slatten was found guilty of first-degree murder by a unanimous federal jury in the death of Ahmed Haithem Ahmed Al Rubia’y.

Slatten, 35, wearing a blue suit and blue tie, was smiling on and off throughout the short hearing, and shrugged to his attorneys when he heard the verdict. No sentencing date has been set.

Slatten was first charged in 2008 along with three other contractors for Blackwater, a private military company, but that case was thrown out.

When the case was brought back in late 2013, Slatten was convicted of first-degree murder and sentenced to life in prison. The other three guards were convicted of charges including manslaughter and attempted manslaughter.

The four men were part of a Blackwater security team code-named Raven 23, who shot 31 innocent Iraqis in the traffic circle of Nisur Square in September 2007. The shooting happened after a car bomb exploded in downtown Baghdad.

Fourteen of the Iraqis, including women and children, died.

Prosecutors in the 2013 trial said Slatten was the person who “initiated the entire incident” when he fired the first shots “without justifications.”

But in 2017, the U.S. Court of Appeals threw out Slatten’s murder conviction and said he deserved a new trial.

That second trial ended in September 2018 when a mistrial was declared after weeks of the jury being unable to reach a unanimous verdict.

Blackwater was founded by Erik Prince, who is the brother of Education Secretary Betsy Devos. Since the 2007 shooting, Prince sold the company, which reorganized and now exists as Academi.

Gary Grumbach reported from Washington, D.C., Elisha Fieldstadt reported from New York.