The Marine Corps has dropped all charges against a captain accused of failing to investigate the deaths of 24 civilians and another Marine accused in some of the killings, the Corps announced Thursday.

Capt. Randy W. Stone, 35, a battalion lawyer from Dunkirk, Md., was one of four officers charged with failing to adequately probe the killings.

"It is clear to me that any error of omission or commission by Capt. Stone does not warrant action under the Uniform Code of Military Justice," Lt. Gen. James Mattis wrote.

The Corps also announced that charges had been dismissed against Lance Cpl. Justin Sharratt, who was accused of murdering three brothers in the assault that followed a deadly roadside bombing of U.S. troops.

The decision to drop the charges against Sharratt followed an earlier recommendation from Lt. Col. Paul Ware, a hearing officer.

"The government version is unsupported by independent evidence," Ware wrote. "To believe the government version of facts is to disregard clear and convincing evidence to the contrary."

Prosecutors alleged Sharratt and other members of his battalion engaged in a revenge-motivated assault on Iraqi civilians after a roadside bomb killed a fellow Marine. Sharratt contended the Iraqi men he confronted were insurgents and at least one was holding an AK-47 rifle when he fired at them.

Ware said prosecution of Sharratt could set a "dangerous precedent that ... may encourage others to bear false witness against Marines as a tactic to erode public support of the Marine Corps and its mission in Iraq."

"Even more dangerous is the potential that a Marine may hesitate at the critical moment when facing the enemy," Ware said.

Besides Sharratt, two other enlisted men were charged with murder. Four officers, including Stone, were accused of failing to investigate the deaths.