WASHINGTON -- Four former Blackwater security guards were convicted Wednesday in the 2007 shootings of more than 30 Iraqis in Baghdad, an incident that inflamed anti-American sentiment around the globe and was denounced by critics as an illustration of a war gone horribly wrong.

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. A lawyer for one of them quickly said he expected to appeal.

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.

Former Blackwater Worldwide guard Nicholas Slatten leaves federal court in Washington, Wednesday, June 11, 2014. Cliff Owen, AP

CBS News' Paula Reid reports that the verdict sheet asked the jury -- comprised of eight women and four men -- to make more than 100 separate findings pertaining to 33 counts against the four defendants.

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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."

Former Blackwater guards Nicholas Slatten, Dustin Heard, Paul Slough and Evan Liberty appear in court in Washington, D.C., October 22, 2014. William Hennessy, Jr.

However, 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 Blackwater to protect American diplomats in Baghdad, the Iraqi capital, and elsewhere in the country. Blackwater convoys of four 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 an 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.

The guards, the prosecution said, held "a grave indifference" to the death and injury that their actions probably would cause Iraqis. 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.

The four men had been charged with a combined 32 counts in the shootings and the jury was able to reach a verdict on all of them, with the exception of three against Heard. The prosecution agreed to drop those charges.

Slough was convicted of 13 counts of voluntary manslaughter and 17 counts of attempted manslaughter. Liberty was convicted of eight counts of voluntary manslaughter and 12 counts of attempted manslaughter. Heard was convicted of six counts of voluntary manslaughter and 11 counts of attempted manslaughter.

Voluntary manslaughter carries a penalty of up to 15 years in prison and attempted manslaughter carries a maximum seven years in prison.

All three were also convicted on gun charges that carry a mandatory minimum sentence of 30 years in prison.

Prosecutors said that from a vantage point inside his convoy's command vehicle, Slatten aimed his SR-25 sniper rifle through a gun portal, killing the driver of a stopped white Kia sedan, Ahmed Haithem Ahmed Al Rubia'y.

In 2007, CBS News interviewed Ali Khalaf Salman, a police officer who was an eyewitness to the shooting. He said that he heard a woman scream and he rushed to the car.

"She started screaming 'My son' and she held on to him," he said. "I opened the door and I found that he has been shot three times in the head."

At the trial, two Iraqi traffic officers and one of the shooting victims testified the car was stopped at the time the shots were fired. The assertion that the car was stopped supported the prosecution argument that the shots were unwarranted.

Defense lawyers pressed their argument that other Blackwater guards - not Slatten - fired the first shots at the Kia sedan and that they did so only after the vehicle moved slowly toward the convoy, posing what appeared to be a threat to the Blackwater guards' safety.