Murder charges against a US marine accused of killing three Iraqi civilians in Haditha two years ago have been dropped, the US military has said.
L/Cpl Justin Sharratt was among several accused of going on a rampage in which 24 Iraqis were killed after a roadside bombing killed one US marine.
Investigators said the allegations were not supported by independent evidence.
Two more marines still face murder charges. Three others have been charged with failing to investigate the deaths.
A fourth, Capt Randy W Stone, had his charges of failing to investigate the killings adequately dropped on Thursday.
Charges against another murder suspect, Sgt Sanick Dela Cruz, were dropped in April in exchange for his testimony.
In a ruling released at Camp Pendleton, California, Lt Gen James Mattis said that an investigating officer's report on L/Cpl Sharratt's case, did not support a referral to court-martial.
"To believe the government version of facts is to disregard clear and convincing evidence to the contrary," said the investigator, Lt Col Paul Ware.
L/Cpl Sharratt has never denied killing the three Iraqi men, but insists they were insurgents and that at least one was holding an AK-47 rifle when he opened fire.
Twenty-four Iraqi civilians, including three women, seven children and several elderly men, died at Haditha, in Anbar province, on 19 November 2005.
The US military at first reported that the Iraqis had been killed by the improvised explosive device (IED) that killed L/Cpl Miguel Terrazas, or in a subsequent gunfight with insurgents.
But Iraqi witnesses said the US troops shot dead five unarmed men in a car when they approached the scene of the bombing in a taxi.
They were then accused of killing 19 other civilians in three houses nearby over the next few hours.
Despite the accusations, there was no full US investigation into what happened until January 2006, when video footage emerged of the aftermath taken by a local human rights activist.
After a report in Time magazine showed flaws in the initial marine statement, a preliminary investigation was begun.
The inquiry confirmed civilians had been shot in their homes, but described the deaths as "collateral damage".
The report prompted the US Naval Criminal Investigation Service (NCIS) to determine the motives behind the killing.
In December, military authorities charged four marines with unpremeditated murder and another four with failing to properly report or investigate the deaths.
The Haditha inquiry is the biggest US criminal case involving unlawful Iraqi civilian deaths to come out of the war so far.
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