CAMP PENDLETON — The Marine Corps has dropped murder charges and  granted immunity to a sergeant accused of taking part in actions that led to the deaths of two dozen civilians in the Iraqi city of Haditha in 2005, a development that could bolster the government’s prosecution of other defendants.

The withdrawal of charges against Sgt. Sanick Dela Cruz was approved by Marine Lt. Gen. James Mattis “after the government balanced the low level of culpability in the alleged crimes against the value of his testimony,” according to a statement issued at Camp Pendleton.

Gary Solis, a former Marine Corps attorney and now a military law professor at Georgetown University, said giving immunity to the 24-year-old Dela Cruz does not bode well for the other enlisted men.

While enlisted men are charged with crimes of violence, four officers — including Capt. Lucas McConnell of Napa — face charges related to the subsequent reporting of the incident. McConnell faces one count of dereliction of duty for what prosecutors say was a failure to fully report the incident to superiors. His lawyer, Southern California’s Kevin McDermott, has repeatedly asserted McConnell’s innocence.

In a telephone interview, Solis said the enlisted men remaining in the case now face tougher odds.

“The defense of the other men just got a lot more difficult,” he said. “The government now has testimony from an inside man who presumably will testify against the others.”

Brian Rooney, an attorney for the highest-ranking man charged in the case, Lt. Col. Jeffrey Chessani, said after reading the investigatory documents that he thought Dela Cruz had “a lot to worry about.”

“I suspect they had him over a barrel,” Rooney said, adding the development wasn’t surprising and probably would not have much impact on the case against Chessani, who was dismissed from his post as commander when the battalion returned from Iraq in April 2006.

Dela Cruz was charged on Dec. 21 with five counts of what the military calls unpremeditated murder for shooting five men who emerged from a taxi that drove up shortly after a Humvee was destroyed by a roadside bomb in Haditha on Nov. 19, 2005. The bombing killed Lance Cpl. Miguel Terrazas of Texas.

Three other enlisted men still face murder charges, including the squad leader, Staff Sgt. Frank Wuterich, who is accused of killing 19 of the 24 civilians who died at the hands of the troops from the 3rd Battalion, 1st Marine Regiment based at Camp Pendleton. The incident drew worldwide condemnation when it was first reported in March 2006.

In addition to Wuterich, the enlisted defendants are lance cpls. Justin Sharratt and Stephen Tatum. Sharratt is charged with three counts of unpremeditated murder. Tatum is charged with two counts of unpremeditated murder, four counts of negligent homicide and one count of assault.

The officers — Chessani, McConnell, Capt. Randy Stone and 1st Lt. Andrew Grayson — face dereliction of duty and related charges for allegedly failing to properly investigate the initial reports of the deaths in Haditha.

Mark Zaid, an attorney for Wuterich, said he remains confident in the defense case.

“We are prepared to respond to any and all allegations, and in that sense the immunity deal has changed nothing,” Zaid said. “I do have some concern that if the principles the government is attempting to espouse — that all the guilty parties should be punished for alleged misconduct — and their case is so strong, why are they making a deal?”

Zaid also said documents show Dela Cruz gave investigators conflicting statements.

“So if there is something new to come from him, it would probably be inconsistent with other statements he has given,” Zaid said, adding that attorneys for all the defendants anticipated that one or more would make a deal with prosecutors.

Dela Cruz’s attorney, Daniel Marino, did not return telephone calls seeking comment.

A native of Chicago, Dela Cruz was on his third tour in Iraq when the incident took place. Had he been tried and convicted of murder, Dela Cruz could have faced life in prison and a dishonorable discharge. Dela Cruz also is alleged to have urinated on one of the slain men.

Mattis, the convening authority over the case as head of Marine Corps forces in the Middle East, approved the deal with Dela Cruz on April 2, but the Marine Corps did not disclose the deal until now because it first wanted to notify all the attorneys involved in the case.

Wuterich has acknowledged ordering the shooting of five men who emerged from the taxi and ordering the assault of nearby homes where 19 others, including several women and children, were killed.

An Article 32 hearing for Wuterich, at which the government and defense present their theories of the case, is tentatively set to begin June 4. The officer who presides over that session will ultimately decide whether to recommend that Mattis order the case to court-martial.

Wuterich and attorneys for the other men charged with homicide contend that while the deaths were regrettable, the Marines’ actions were within the military’s rules of engagement and their clients are innocent of any criminal act.