Murtha, a former Marine who has criticized the Bush administration's conduct of the war, repeated his view that the war cannot be won militarily and needs political solutions, which he said were damaged by such incidents involving the U.S.

The incident at Haditha has sparked two investigations ¡ª one into the deadly encounter itself and another into whether it was the subject of a cover-up.

The second, noncriminal investigation is examining whether Marines sought to cover up what happened that day and, in doing so, lied about having killed civilians without justification. The Marine Corps had initially attributed 15 civilian deaths to the car bombing and a firefight with insurgents, eight of whom the Marines reported had been killed.

A defense official, who spoke on condition of anonymity because he was not authorized to speak publicly, told The Associated Press on Friday that evidence gathered so far strongly indicated that the Haditha killings were unjustified.

Early this year, a videotape of the aftermath of the incident, showing the bodies of women and children, was obtained by Time magazine and Arab television stations. The military then undertook another investigation.

Sen. John Warner, R-Va., chairman of the Senate Armed Services Committee, said he would hold hearings on the incident but cautioned against reaching conclusions until the military completed its investigation.

"There is this serious question, however, of what happened and when it happened and what was the immediate reaction of the senior officers in the Marine Corps when they began to gain knowledge of it," Warner said on ABC.

The Naval Criminal Investigative Service investigation into the shootings is ongoing. Whether violations of the Uniform Code of Military Justice, including murder, would be pursued would be determined by a senior Marine commander in Iraq.

The NCIS also is conducting a criminal investigation into another incident, the April 26 death of an Iraqi civilian involving Marines in Hamandiyah, west of Baghdad.