CAMP PENDLETON, Calif. — Hours before his court-martial was set to begin, all charges were dismissed Friday against one of two remaining enlisted marines involved in a combat action that killed 24 Iraqis in Haditha in 2005, the Marine Corps announced.

With little public explanation, a Marine general in charge of the prosecution dropped the charges against Lance Cpl. Stephen B. Tatum, who was among four enlisted marines originally charged with murder in the case.

The charges against him had been reduced to involuntary manslaughter, reckless endangerment and aggravated assault for what prosecutors said was his role in shooting a group of unarmed women and children.

As a result of the dismissal, Corporal Tatum’s squad leader, Staff Sgt. Frank D. Wuterich, is the only remaining enlisted marine, and the only infantryman who was involved in the Haditha killings, still facing charges in the case. His trial is likely to begin this summer, lawyers said.

Charges against the other two enlisted marines were dropped previously.

A court-martial of an officer, Lt. Col. Jeffrey Chessani, in charge of the battalion Sergeant Wuterich and Corporal Tatum were part of, is to begin in late April. Colonel Chessani is charged with dereliction of duty for failing to properly investigate the Haditha killings.

The killings occurred on Nov. 19, 2005, when a squad of infantrymen from Third Battalion, First Marines, swept through a group of Iraqi homes in search of attackers after a roadside bomb exploded near their convoy, killing a marine. Over a period of hours, marines assaulted four Iraqi homes, killing 24 people, almost all unarmed.