A federal court in Washington DC has sentenced a former Blackwater security guard to life in prison and three others to 30 years in jail for their roles in a 2007 shooting that killed 14 Iraqi civilians in Baghdad and caused an international uproar.

Nicholas Slatten received a life sentence for first-degree murder, while Dustin Heard, Evan Liberty and Paul Slough were imprisoned for charges that included manslaughter.

The ex-guards were convicted in October after a long legal fight over the deadly attack at the crowded Nisoor traffic circle in downtown Baghdad.

US District Judge Royce Lamberth announced the sentences after a day-long hearing at which defence lawyers had argued for leniency, and prosecutors asked that those sentences, the minimums mandatory under the law, be made even harsher.

'Without justification'

In a statement, the US Attorney's Office said the prosecution reflected the country's commitment to the rule of law. "In killing and maiming unarmed civilians, these defendants acted unreasonably and without justification," the statement said.

"In combination, the sheer amount of unnecessary human loss and suffering attributable to the defendants' criminal conduct on Sept 16, 2007, is staggering."

Andrew McCabe, the assistant director in charge of the FBI's Washington field Office, said: "These sentencings are the result of the enduring resolve by law enforcement to protect victims of violent crime." 

"The results of this case demonstrate that the FBI will investigate violations of US law no matter where they occur in order to bring justice to innocent victims," he added.

Prosecutors said the shooting was unprovoked, though defence lawyers countered that the men were targeted with gunfire from fighters and Iraqi police, and shot back in self-defence.

Al Jazeera correspondent Shihab Rattansi, reporting from Washington, said the sentencing will not bring an end to the legal wrangling, which began even before the guards were first charged in 2008.

"Because of the lack of a clear framework of accountability for US security contractors, these men are appealing their convictions," our correspondent said.

"It is clear that the Obama administration wanted to make an example of this case; but it is spending tens of billions of dollars on private military contractors, including the corporate descendants of Blackwater, while there remain unresolved questions on oversight, transparency and accountability."

Source: Al Jazeera and agencies