Former Blackwater Worldwide security guards Paul Slough, right, and Nicholas Slatten leave federal court in Salt Lake City in 2008. (Douglas C. Pizac/AP)

Federal prosecutors called on a federal judge to impose lengthy prison terms at sentencing Monday for four Blackwater Worldwide guards convicted in the 2007 shooting that killed 14 unarmed Iraqis and injured others in a Baghdad traffic circle.

Paul A. Slough of Keller, Tex.; Evan S. Liberty of Rochester, N.H.; and Dustin L. Heard of Knoxville, Tenn., were found guilty by a District federal jury in October of multiple counts of manslaughter and attempted manslaughter in the Sept. 16, 2007, incident at Baghdad’s Nisour Square.

A fourth man, Nicholas A. Slatten of Sparta, Tenn., was convicted of murder in the incident, in which American security contractors fired machine guns and grenades into halted noonday traffic, a low point of the U.S. war in Iraq that sent relations between the two countries into a crisis.

Jurors found that the defendants, at the time among 19 Blackwater guards providing security for State Department officials in Iraq, shot recklessly and out of control after one of them falsely claimed that their convoy, called Raven 23, was threatened by a car bomber.

The guards claimed they acted in self-defense under incoming AK-47 gunfire as they cleared a path back to the nearby Green Zone for another Blackwater team that was evacuating a U.S. official from a nearby car bombing.

The verdicts capped a years-long effort by the U.S. government to address accountability for security contractors’ conduct on the battlefield, which became symbolized by the Blackwater case. In sentencing documents, the four defendants sought leniency, saying they have been unfairly singled out for harsh treatment for a wartime tragedy.

Slatten faces a mandatory sentence of life in prison without parole for first-degree murder before U.S. District Judge Royce C. Lamberth, an Army veteran and Reagan appointee who served as chief district judge from 2008 to 2013, when he took senior status.

Federal prosecutors urged Lamberth to exceed federal guidelines and sentence the three others to longer than the mandatory minimum of 30-year terms they face for using military firearms while committing a felony.

In total, the U.S. government sought a 57 -year sentence for Slough, also convicted of 13 counts of manslaughter and 17 counts of attempted manslaughter; 51 years for Liberty, also convicted of eight counts of manslaughter and 12 counts of attempted manslaughter; and 47 years for Heard, also convicted of six counts of manslaughter and 11 counts of attempted manslaughter.

“The crimes here were so horrendous – the massacre and maiming of innocents so heinous – that they outweigh any factors that the defendants may argue form a basis for leniency,” wrote attorneys for the national security section of U.S. Attorney’s Office for the District, led by Gregg A. Maisel.

“This is especially true here, where the defendants have shown no remorse for their actions,” Maisel wrote. “Indeed, the defendants have not accepted responsibility for their criminal actions whatsoever and, to this day, have denied any wrongdoing.”

The defendants, all military veterans with no or minimal criminal records, cited their honorable intentions while under extraordinary duress — facing an out-of-uniform guerrilla insurgency in a foreign war zone — and asked for modest terms that might permit them to return to spend productive years in society and with their families.

Attorneys for all four men challenged the legality of the jurors’ verdict and Slough, Liberty and Heard asked the judge to set aside the 3o-year minimum requirement as unconstitutionally harsh and “grossly disproportionate” given the “unprecedented circumstances” of the case.

Defendants said that the case is the first in which the U.S. government prosecuted its own security contractors for the firearms violation, which involve weapons given them by the government to do their jobs in a war zone.

“Nicholas A. Slatten, like many young men and women of his generation, dedicated and sacrificed the best years of his youth in honorable service to his country. . . . He is an innocent man,” said Slatten’s attorneys, with the Harris, Wiltshire & Grannis LLP law firm, who have appealed the verdict saying he did not cause the tragedy or kill any innocent people.

Heard “presents no threat to society,” his attorney, David Schertler, of the Schertler & Onorato LLP law firm in a sentencing plea to Lamberth. He “served his country honorably, and his crimes occurred under circumstances in which no person can be expected to make pristine judgments,” Schertler said.

Liberty’s attorney, William Coffield, of the Berliner, Corcoran & Rowe LLP law firm, wrote, “All of the offenses for which Mr. Liberty has been convicted occurred within the span of a few short and chaotic minutes. . . . His life, as he built it, is over.”

In asking for leniency from Lamberth, the defendants presented letters attesting to their character and community contributions from parents and siblings, wives and children, former service mates, employers and clergy, among others.

Brian M. Heberlig, head of Slough’s defense team at the Steptoe & Johnson LLP law firm, called his client an exemplary soldier and contractor whose judgment often saved the lives of Iraqi civilians.

“Mr. Slough has dedicated his life to serving his country, uplifting his family, and to helping others through his Christian faith,” Heberlig wrote.

Heberlig wrote that military authorities “familiar with the vagaries of war” treated differently U.S. service members accused of killing 25 unarmed Iraqi in a 2005 raid on their home in Anbar province.

Assault and manslaughter charges were dismissed against six U.S. Marines in the Haditha incident, another was acquitted and an eighth man was convicted of dereliction of duty, receiving a reduction in rank and no jail time.

The U.S. government brought civilian charges in 2008 against six Blackwater employees. One, Jeremy Ridgeway, pleaded guilty to manslaughter and testified against the others. Charges were dropped against another man, Donald Ball.

The remaining four defendants claimed the violence was triggered by Ridgeway, who a prosecutor conceded suffered from post-traumatic stress disorder and “lost it” in Iraq, and by the convoy’s team leader, Jimmy Watson.

Watson and two other members of the Blackwater team were granted limited immunity by the government to testify against their former colleagues.

The founder of Blackwater, Erik Prince, eventually left the company, which was renamed Xe Services, then later sold and renamed Academi.