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Andrew Harnik, Associated Press
Family members, friends and supporters of four former Blackwater security guards follow Steptoe & Johnson attorney Brian Heberlig, center, representing Paul Slough of Keller, Texas, as they depart the Barrett Prettyman Federal Courthouse in Washington, Monday, April 13, 2015, following sentencing for four former Blackwater security guards in connection with a 2007 shooting of civilians in Iraq. U.S. District Judge Royce Lamberth sentenced Nicholas Slatten to life in prison while Slough, Evan Liberty of Rochester, N.H., and Dustin Heard of Knoxville, Tenn., were convicted of manslaughter and received sentences of 30 years plus one day.

WASHINGTON — Defense lawyers are vowing to appeal the convictions of four former Blackwater security guards after a federal judge handed down lengthy prison terms for their roles in a 2007 shooting of unarmed civilians in Iraq.

Attorneys identified several issues Monday as likely forming the basis of an appeal, including vindictive prosecution and whether State Department contractors could be charged under a federal law that covers the overseas crimes of Defense Department civilian employees.

The move comes after U.S. District Judge Royce Lamberth sentenced former guard Nicholas Slatten to life in prison and three others to 30-year terms for their roles in the shootings that killed 14 Iraqi civilians and wounded 17 others.

Slatten, who witnesses said was the first to fire shots in the melee, was sentenced to life after being convicted last October of first-degree murder. The three other guards — Paul Slough, Evan Liberty and Dustin Heard — were each sentenced to 30 years and one day in prison for charges that included manslaughter, attempted manslaughter and using firearms while committing a felony.

The incident in Baghdad's Nisoor Square strained U.S.-Iraq relations and caused an international uproar over the use of private security guards in a war zone.

Lamberth announced the sentences after a daylong hearing at which defense lawyers had argued for leniency and presented character witnesses for their clients. At the same time, prosecutors asked that those sentences — the minimums mandatory under the law — be made even harsher. He rejected both requests.

Appearing in court wearing leg shackles and prison garb, the former contractors insisted they were innocent.

"The verdict is wrong, you know that I am innocent, sir," Slatten told the judge.

"I feel utterly betrayed by the same government I served honorably," Slough said.

But Lamberth said he fully agreed with the jury's guilty verdicts and praised the Justice Department and the FBI for investigating the shooting and putting the truth "out there for the world to see."

Nearly 100 friends and relatives packed the courtroom to show support for the men, with many openly weeping throughout the proceedings. Several came to the podium, some choking back tears, to speak glowingly of the men they knew as role models and patriots who only wanted to help serve their country.

Assistant U.S. Attorney Patrick Martin described the shooting as an unprovoked ambush of civilians and said the men haven't shown remorse or taken responsibility. Defense lawyers countered that the men were targeted with gunfire and shot back in self-defense with guns the State Department had provided them for safety.

"This was no unprovoked massacre, and we'll never accept that it was," said Brian Heberlig, attorney for Slough.

Mohammad Kinani Al-Razzaq spoke in halting English about the death of his 9-year-old son as a photo of the smiling boy, Ali Mohammed Hafedh Abdul Razzaq, was shown on courtroom monitors. He demanded the court show Blackwater "what the law is."

"What's the difference between these criminals and terrorists?" Razzaq said.

Baghdad resident, Bara Saadoun Ismael, who received two bullets in his abdomen in addition to 60 pieces of shrapnel in different parts of his body in 2007, is not satisfied with the verdict, demanding capital punishment.

"This verdict is less than what they deserve," the 36-year old taxi driver told The Associated Press in a phone interview in Baghdad. "They did hurt us a lot and for what they did to us they must face execution."

The shrapnel wounds "make it very hard to drive or sit for long hours and also hurt me in hot and cold weather," he said.

Defense lawyers argued for mercy, saying decades-long sentences would be unconstitutionally harsh for men who operated in a stressful, war-torn environment and who have proud military careers and close family ties.

But Lamberth said he would not deviate from the mandatory minimum sentences, noting that similarly stiff penalties have been applied to police officers who commit crimes while carrying automatic weapons as part of their jobs.

Defense attorney David Schertler, who represents Heard, said he would argue on appeal that the sentences violate the Constitution's ban on cruel and unusual punishment given the circumstances.

Thomas Connolly, who represents Slatten, said his client would appeal on a claim of vindictive prosecution. Slatten originally was charged with manslaughter in 2007, but an appeals court threw out the charge and the statute of limitations lapsed. Connolly says prosecutors then unfairly charged his client with a more serious charge of murder.

In a statement, the U.S. Attorney's office said the case shows "that the FBI will investigate violations of U.S. law no matter where they occur in order to bring justice to innocent victims."

Slatten, 31, is from Sparta, Tennessee; Slough, 35, from Keller, Texas; Liberty, 32, from Rochester, New Hampshire; and Heard, 33, from Maryville, Tennessee.

Associated Press writer Sinan Salaheddin in Baghdad contributed to this report.