The Blackwater guards are scheduled to appear for arraignment Tuesday afternoon in U.S. District Court on manslaughter and weapons charges in the shootings.

Expected to enter not guilty pleas are former Marines Donald Ball of West Valley City, Utah; Dustin Heard of Knoxville, Tenn.; Evan Liberty of Rochester, N.H.; and Army veterans Nick Slatten of Sparta, Tenn., and Paul Slough of Keller, Texas.

A sixth guard — Jeremy Ridgeway of California — has pleaded guilty to one count each of manslaughter, attempted manslaughter, and aiding and abetting. He has agreed to cooperate with investigators.

Prosecutors said the men unleashed a gruesome attack on unarmed Iraqis, including women, children and people trying to escape. But defendants contend they opened fire after coming under attack when a car in a State Department convoy they were escorting broke down.

Blackwater radio logs made available to The Associated Press by a defense attorney in the case last month raised questions about prosecutors' claims that the guards' shooting was unprovoked. The log transcripts describe a hectic eight minutes in which the guards repeatedly reported incoming gunfire from insurgents and Iraqi police.

The North Carolina-based Blackwater is the largest contractor providing security in Iraq. Most of its work for the State Department is in protecting U.S. diplomats in Iraq. The company has not been charged in connection with the shooting.