CAMP PENDLETON, Calif. -- Charges were dismissed against a Marine officer accused of covering up and failing to investigate the deaths of 24 Iraqi civilians in Haditha, it was announced Tuesday.

Capt. Lucas M. McConnell, the commanding officer of Company K, 3rd Battalion, 1st Marine Regiment, at the time of the Nov. 19, 2005, deaths, was charged last December with dereliction of duty.

Lt. Gen. James Mattis ordered the dismissal of the charges last Wednesday. He also issued a grant of immunity and ordered McConnell to cooperate with all parties in the case.

Lance Cpl. Stephen B. Tatum, Lance Cpl. Justin Sharratt, Staff Sgt. Frank Wuterich and Sgt. Sanick Dela Cruz and four Marine officers were originally accused in the deaths of the two dozens Iraqis.

The enlisted men were charged with murder; the officers were charged with failing to report and investigate the incident.

Charges were previously dropped against Dela Cruz, Sharratt and Stone.

The Marine Corps is still deciding whether to court-martial Tatum, Wuterich, 1st Lt. Andrew Grayson and Lt. Col. Jeffrey Chessani.

The deaths of the two dozen Iraqi civilians came after a bomb attack killed a Marine and injured two others.

The defendants claim the civilians got caught up in combat between U.S. troops and insurgents.

Earlier this month, Secretary of the Navy Donald Winter issued letters of censure to Maj. Gen. Richard A. Huck, Col. Stephen W. Davis and Col. Robert G. Sokoloski for their actions following the Haditha slayings.