A U.S. jury returned guilty verdicts for all four former Blackwater security guards charged in the 2007 shootings of more than 30 Iraqis in Baghdad.

The jury in Washington found Nicholas Slatten guilty of first-degree murder, and the three other three guards — Paul Slough, Evan Liberty and Dustin Heard — guilty of at least three counts of voluntary manslaughter.

The four men were charged with a combined 33 counts in the shootings, but the jury had reached verdicts on only part of the charges after weeks of deliberations. District Court Judge Royce C. Lamberth allowed the jury to announce the verdicts agreed upon, with the expectation jurors would continue deliberating on the other counts.

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

The State Department hired Blackwater to protect American diplomats in Baghdad, the Iraqi capital, and elsewhere in the country. Blackwater convoys of four heavily armoured vehicles operated in risky environments where car bombs and attacks by insurgents were common.

Slatter was charged with first-degree murder; the others were charged with voluntary manslaughter, attempted manslaughter and gun charges.

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

The maximum sentence for conviction of first-degree murder is life imprisonment. The gun charges carry mandatory minimum prison terms of 30 years. The maximum prison term for involuntary manslaughter is eight years; for attempted manslaughter it is seven years.

The trial 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.

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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-defence. Federal prosecutors said there was no incoming gunfire and that the shootings by the guards were unprovoked.

The prosecution focused on the defendants' intent, contending that some of the Blackwater guards harboured 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.

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.

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.

Defence 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.

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Once the shooting started, hundreds of Iraqi citizens ran for their lives.

It was "gunfire coming from the left, gunfire coming from the right," prosecutor Anthony Asuncion told the jury in closing arguments.

One of the government witnesses in the case, Blackwater guard Jeremy Ridgeway, pleaded guilty to killing the driver's mother, who died in the passenger seat of the white Kia next to her son.

The maximum sentence for conviction of first-degree murder is life imprisonment. The gun charges carry mandatory minimum prison terms of 30 years. The maximum prison term for involuntary manslaughter is eight years; for attempted manslaughter it is seven years.