Local witnesses and human rights activists say marines raided three houses. Five men in a car were also shot. Here are highlights of the case:
November 19, 2005 - A roadside bomb kills Lance Corporal Miguel "TJ" Terrazas, 20, from El Paso, Texas, during a patrol by Kilo Company, 3rd Battalion, 1st Marine Regiment, 1st Marine Division in Haditha. In the following hours, 24 Iraqis are killed. Marine investigators inspect the scene and take photographs.
November 20 - Military says roadside bomb killed a marine and 15 civilians. Captain Jeffrey Pool says in statement: "Iraqi army soldiers and [US] marines returned fire killing eight insurgents."
January 2006 - Journalism student Taher Thabet, via an Iraqi human rights group, passes video of bodies and homes where they died to Time magazine. Time says Pool dismisses it as al-Qaeda propaganda. But Baghdad military spokesman Lieutenant-Colonel Barry Johnson recommends investigation into possible foul play.
February 14 - Lieutenant-General Peter Chiarelli, the No. 2 US commander in Iraq, initiates a preliminary investigation.
March 9 - Chiarelli directs further review of the incident by the Naval Criminal Investigation Service (NCIS).
March 27 - Time magazine publishes survivors' allegations that marines ran amok after Terrazas's death. Iraqi human rights group issues the video showing residents describing rampage and bodies, including that of a child of about three. US military confirms civilians were shot, not killed by roadside bomb.
April 7 - Three officers, 3rd Battalion commander Lieutenant-Colonel Jeffrey Chessani, Kilo Company commander Captain Lucas McConnell and Captain James Kimber are relieved of command.
May 26 - US defence official says marines face charges, including for murder, after media reports that investigators are about to recommend charges against about a dozen marines, including murder and lying in reports.
- The NCIS investigation is not complete and no final decisions on charges have been made, defence officials say.
- John Warner, chairman of the Senate armed services committee, says it will probe incident and its aftermath.
- John Murtha, Democratic congressman and former marine and war critic, says the military attempted a cover-up and accuses the marines of killing "in cold blood".
- Some US media compare Haditha to the 1968 My Lai massacre in Vietnam, when US soldiers ran amok in the village, and killed some 500 people, mostly women, children and old men.
- US politicians briefed on the investigation are quoted as saying several marines, led by a sergeant, went from house to house killing people and also killed four students and a taxi driver in a car that approached the scene. Photographs of the corpses suggested some victims had been kneeling when killed.
In addition to Terrazas, Iraq's Hammurabi human rights organisation listed the dead of November 19 as follows:Marines, who have suffered the worst casualties among US forces in the Iraq war, mounted several offensives in 2005 in the region around Haditha, where they have often been hit by roadside bombs, the most effective killer of US troops.
A roadside bomb killed 14 marines in August 2005 near Haditha and destroyed their armoured amphibious assault vehicle. Six were killed by fighters in the town, and a seventh was killed by a car bomb in nearby Hiyt a few days earlier.
- House 1: Asmaa Salman Raseef, 32, Abdullah Waleed Abdul Hameed, child, Abdul Hameed Hasan Ali, late 70s, Waleed Abdul Hameed Hassan, 35, Rasheed Abdul Hameed Hassan, 30, Khameesa Toama Ali, 65.
- House 2: Younis Salim Raseef, 41, Aida Yaseen Ahmed, 35, Muhammad Younis Salim, child, Noor Younis Salim, 14, Sabaa Younis Salim, 9, Aisha Younis Salim, 2, Zainab Younis Salim, 3, Huda Yaseen Ahmed, 28.
- Car: Ahmed Finer Muslih, 25, the taxi driver, Khalid Oyada Abid, 27, Wajdi Oyada Abid, 22, Akram Hameed Flayeh, 21, Muhammad Fatal Ahmed, 21.
- House 3: Jamal Ayed Ahmed, 41, Chassib Ayed Ahmed, 27, Marwan Ayed Ahmed, 28, Kahtan Ayed Ahmed, 24.
Haditha is a Euphrates valley farming town 200km northwest of Baghdad in Iraq's western al-Anbar province, the heartland of the Sunni Arab uprising seeking to topple the Shia-led government backed by the United States.