Lt. Col. Jeffrey R. Chessani faces charges of dereliction of duty and violation of a lawful order for allegedly failing to accurately report and investigate the Nov. 19, 2005, killings of 24 Iraqis.
Chessani is the most senior U.S. serviceman since the Vietnam War to face a court-martial for actions or decisions made in combat, said Gary Solis, a former Marine Corps prosecutor and judge who teaches law of war at Georgetown University Law Center.
Lance Cpl. Stephen B. Tatum faces a court-martial on charges of involuntary manslaughter, reckless endangerment and aggravated assault.
The decision by Lt. Gen. James Mattis to send Tatum to court-martial comes after the investigating officer said last month that the evidence was too weak to prosecute him. But Tatum will not be tried on the murder count he originally faced.
Tatum, of Edmond, Okla., shot and killed civilians, but "he did so because of his training and the circumstances he was placed in, not to exact revenge and commit murder," Lt. Col. Paul Ware wrote last month in recommending he not face court-martial.
The decision to send Chessani to trial mirrored the conclusion the hearing officer reached at his preliminary hearing. Col. Christopher Conlin said Chessani "failed to thoroughly and accurately report and investigate a combat engagement that clearly needed scrutiny."
In his report, Conlin, an infantry officer, blasted Chessani for failing to go to the scene of the November 2005 killings immediately after they had occurred, even though he knew 24 "neutrals" were dead.
"To not have made every attempt to be on scene as this action developed, or to not have at least reviewed this action in detail ... is in itself negligent," Conlin wrote. "The fact that one fireteam was solely responsible for 24 deaths in all direct fire actions should have solicited more than passing interest from the senior leadership of the battalion."
At Chessani's preliminary hearing, held in June at Camp Pendleton, several witnesses testified local Iraqis had complained to Chessani in the days after the killings and that he promised to look into what had happened.
But Chessani said he never ordered a formal investigation because he believed the deaths resulted from lawful combat.