The men claimed self-defense, but federal prosecutors argued that they had shown “a grave indifference” to the carnage their actions would cause. All four were ordered immediately to jail.

Their lawyers are promising to file appeals. The judge did not immediately set a sentencing date.

The federal jury found Nicholas Slatten guilty of first-degree murder, the most serious charge in a multi-count indictment. The three other guards — Paul Slough, Evan Liberty and Dustin Heard — were found guilty of multiple counts of voluntary manslaughter, attempted manslaughter and gun violations.

The outcome after a summer-long trial and weeks of jury deliberation appeared to stun the defense.

David Schertler, a lawyer for Heard, said, “The verdict is wrong, it’s incomprehensible. We’re devastated. We’re going to fight it every step of the way. We still think we’re going to win.”

One of those struck by gunfire in the shootings, Hassan Jabir, said in Baghdad that “at last we are hearing good news where justice has been achieved and Blackwater will receive their punishment.” He said there are two bullets still inside his body, one in his hand and one in his back, which doctors have said it would be very risky to remove.

The shootings on Sept. 16, 2007, caused an international uproar over the role of defense contractors in urban warfare.

The State Department had hired Virginia-based Blackwater — since sold and renamed Academi — to protect American diplomats in Baghdad, the Iraqi capital, and elsewhere in the country. Blackwater convoys of heavily armored vehicles operated in risky environments where car bombs and attacks by insurgents were common.

On the murder charge, Slatten could face a maximum penalty of life in prison. The other three defendants could face decades behind bars.

The case was mired in legal battles for years, making it uncertain whether the defendants would ever be tried.

The trial itself focused on the killings of 14 Iraqis and the wounding of 17 others. During the 11-week trial, prosecutors summoned 72 witnesses, including Iraqi victims, their families and former colleagues of the defendant Blackwater guards.

There was sharp disagreement over the facts in the case.

The defendants’ lawyers said there was strong evidence the guards were targeted with gunfire from insurgents and Iraqi police, leading the guards to shoot back in self-defense. Federal prosecutors said there was no incoming gunfire and that the shootings by the guards were unprovoked.

The prosecution contended that some of the Blackwater guards harbored a low regard and deep hostility toward Iraqi civilians and "a grave indifference" to the death and injury that their actions probably would cause. Several former Blackwater guards testified that they had been generally distrustful of Iraqis, based on experience the guards said they had had in being led into ambushes.