The leader of a battalion involved in the killing of 24 Iraqis in Haditha should face a court-martial for dereliction of duty, the investigating officer recommended in a report obtained by The Associated Press on Wednesday.

Lt. Col. Jeffrey Chessani, 43, was charged in December with dereliction of duty and violation of a lawful order for failing to report and investigate the deaths of the men, women and children in the biggest U.S. criminal case involving civilian deaths to come out of the Iraq war.

The investigating officer, Col. Christopher Conlin, wrote that Chessani should face all charges.

"Lt. Col. Chessani failed to do his duty," Conlin wrote. "He failed to thoroughly and accurately report and investigate a combat engagement that clearly needed scrutiny."

The report was provided to the AP by a defense lawyer who asked to remain anonymous because other attorneys in the case had not seen it.

Chessani's defense attorney Brian Rooney did not immediately respond to a phone message.