A sixth guard involved in the attack cut a plea deal with prosecutors, turned on his former colleagues, and admitting killing at least one Iraqi in the 2007 shooting in Baghdad's Nisoor Square. Seventeen Iraqis were killed in the assault, which roiled U.S. diplomacy with Iraq and fueled anti-American sentiment abroad.

The five guards surrendered Monday and were due to ask a federal judge in Utah for bail.

"None of the victims of this shooting was armed. None of them was an insurgent," U.S. Attorney Jeffrey Taylor said. "Many were shot while inside civilian vehicles that were attempting the flee from the convoy. One victim was shot in the chest while standing in the street with his hands up. Another was injured from a grenade fired into a nearby girls' school."

The guards were charged with 14 counts of manslaughter and 20 counts of attempted manslaughter. They are also charged with using a machine gun to commit a crime of violence, a charge that carries a 30-year minimum prison sentence.

The shootings happened in a crowded square where prosecutors say civilians were going about their lives, running errands. Following a car bombing elsewhere in the city, the heavily armed Blackwater convoy sought to shut down the intersection. Prosecutors said the convoy, known by the call sign Raven 23, violated an order not to leave the U.S.-controlled Green Zone.

"The tragic events in Nisoor Square on Sept. 16 of last year were shocking and a violation of basic human rights," FBI Assistant Director Joseph Persichini said.

Witnesses said the contractors opened fire unprovoked. Women and children were among the victims and the shooting left the square littered with blown-out cars. Blackwater, the largest security contractor in Iraq, says its guards were ambushed and believed a slowly moving white Kia sedan might have been a car bomb.

"We think it's pure and simple a case of self-defense," defense attorney Paul Cassell said Monday as the guards were being booked. "Tragically people did die."

Prosecutors said the Blackwater guards never even ordered the car to stop before opening fire. In his plea agreement with prosecutors, former guard Jeremy Ridgeway, of California, admitted there was no indication the Kia was a car bomb.

Though the case has already been assigned to U.S. District Judge Ricardo M. Urbina in Washington, the guards surrendered in Utah. They want the case moved there, where they would presumably find a more conservative jury pool and one more likely to support the Iraq war.

The indicted guards are Donald Ball, a former Marine from West Valley City, Utah; Dustin Heard, a former Marine from Knoxville, Tenn.; Evan Liberty, a former Marine from Rochester, N.H.; Nick Slatten, a former Army sergeant from Sparta, Tenn.; and Paul Slough, an Army veteran from Keller, Texas.

Ridgeway's sentencing on manslaughter, attempted manslaughter and aiding and abetting has not yet been scheduled.

An afternoon court hearing was scheduled on whether to release the guards. Defense attorneys were filing court documents challenging the Justice Department's authority to prosecute the case. The law is murky on whether contractors can be charged in U.S. courts for crimes committed overseas.

The shootings caused an uproar, and the fledgling Iraqi government in Baghdad wanted Blackwater, which protects U.S. State Department personnel, expelled from the country. It also sought the right to prosecute the men in Iraqi courts.

"The killers must pay for their crime against innocent civilians. Justice must be achieved so that we can have rest from the agony we are living in," said Khalid Ibrahim, a 40-year-old electrician who said his 78-year-old father, Ibrahim Abid, died in the shooting. "We know that the conviction of the people behind the shooting will not bring my father to life, but we will have peace in our minds and hearts."

Defense attorneys accused the Justice Department of bowing to Iraqi pressure .

"We are confident that any jury will see this for what it is: a politically motivated prosecution to appease the Iraqi government," said defense attorney Steven McCool, who represents Ball.

Based in Moyock, N.C., Blackwater is the largest security contractor in Iraq and provides heavily armed guards for diplomats. Since last year's shooting, the company has been a flash point in the debate over how heavily the U.S. relies on contractors in war zones

The company itself was not charged in the case. In a lengthy statement, Blackwater stood behind the guards and said it was "extremely disappointed and surprised" that one of the guards had pleaded guilty.

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Associated Press writers Jennifer Dobner and Paul Foy in Salt Lake City and Sameer N. Yacoub in Baghdad contributed to this report.