A US military jury has acquitted a marine of charges that he helped cover up the killing of 24 unarmed Iraqi civilians in Haditha in 2005.
Lt Andrew Grayson had been charged with obstruction of justice and making false statements - charges he denied.
He had been accused of instructing a sergeant to delete digital photographs of the incident.
Four marines and four officers were initially charged in the case, but the case against five of them was dropped.
The marines were charged with murder and the officers with failing to investigate the deaths.
The trial is being held at Camp Pendleton, a military base in California. Lt Grayson was the first to be tried.
In closing arguments the prosecution claimed Lt Grayson had lied to investigators five times, while the defence said the case was the result of a botched investigation conducted under heavy media scrutiny.
Cheers erupted as his acquittal was announced, the Associated Press news agency reported. The killings occurred after a roadside bomb in Haditha on 19 November 2005 left one marine dead and injured two others.
Library footage of the scene in Haditha following the deaths of civilians
The US military at first reported that the Iraqis had been killed by that explosion, or in a subsequent gunfight with insurgents.
But Iraqi witnesses said the US troops shot dead five unarmed men when they approached the scene of the bombing in a car.
The troops were then accused going to nearby houses and killing 19 other civilians.
There was no full US investigation into what happened until January 2006, when video footage emerged of the aftermath, filmed by a local human rights activist.
A subsequent investigation by Time magazine suggested that most of the dead were shot by marines after the bombing - and in March 2006 a criminal investigation was launched.
The following month, three officers in charge of troops in Haditha were stripped of their command and reassigned.
Those accused of involvement in the incident have maintained they were reacting to insurgent fire.
Two marines still face court martial.
Staff Sgt Frank Wuterich has been charged on nine counts of voluntary manslaughter, and battalion commander Lt Col Jeffrey Chessani has been charged with dereliction of duty and violation of a lawful order.
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