After years of delays, four former guards from the security firm Blackwater Worldwide are facing trial in the killings of 14 Iraqi civilians and the wounding of 18 others.
The guards say they acted in self-defense. Prosecutors say the shootings were unprovoked.
A trial in the nearly seven-year-old case is scheduled to begin with jury selection on Wednesday, barring last-minute legal developments.
Prosecutors plan to call dozens of Iraqis to testify in what the Justice Department says is likely to be the largest group of foreign witnesses ever to travel to the U.S. to participate in a criminal trial.
The violence at the Nisoor Square traffic circle in downtown Baghdad was the darkest episode of contractor violence during the war in Iraq.
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