The United Nations denounced a war crime in Syria when a chilling investigation found that sarin nerve gas was used against civilians including children in three rebel-held suburbs of Damascus.
It was the biggest attack with chemical weapons since Saddam Hussein gassed the Kurdish town of Halabja 25 years ago, the United Nations confirmed.
At the insistence of Syria's regime, the UN mission which investigated the attacks on August 21 was forbidden from identifying the perpetrator.
It did, however, uncover evidence - including the precise weapons used in the assault - which implicates Bashar al-Assad's regime, according to experts.
Presenting the investigation to the Security Council, Ban Ki Moon, the UN Secretary-General, voiced "profound shock and regret at the conclusion that chemical weapons were used on a relatively large scale, resulting in numerous casualties, particularly among civilians and including many children".
Ban said the chilling report had presented overwhelming and indisputable evidence of a war crime.
No one had used poison gas on this scale since Saddam Hussein in 1988, he added.
But Ban declined to apportion blame, saying: "It is for others to decide whether to pursue this matter further to determine responsibility."
The United States has said more than 1400 people died in Ghouta. Its subsequent threat of a military strike has eased following the agreement of a plan with Russia to remove Syria's chemical weapons stock, estimated at more than 1000 tonnes.
The UN inspectors, led by Professor Ake Sellstrom, were in Damascus when the attacks took place. They visited three suburbs and concluded that all suffered bombardment by "surface-to-surface rockets containing the nerve agent sarin".
The clear and convincing evidence came in the form of environmental, chemical and medical samples along with interviews with 50 survivors.
These eyewitnesses reported an attack with shelling followed by the onset of symptoms ranging from blurred vision to vomiting and loss of consciousness. They described how many people were simply incapacitated, found lying on the ground either deceased or unconscious.
Many had been asleep when the rockets fell between 2am and 5am local time, dispersing their toxic cargo. Falling temperatures made the attacks still more deadly.
Instead of rising into the sky, the gas stayed close to the ground and penetrated lower levels of buildings, including the basements where people often slept for shelter.
The UN mission did not compile a death toll, saying only that the "relatively large scale" attack happened "against civilians, including children". In all, the experts visited the locations where five rockets had exploded.
The experts identified two types of artillery-launched rocket: the M14 and the 330mm.
Both are in the armoury of Assad's forces, which also possesses one of the world's biggest stockpiles of sarin nerve gas.
Whether the rebels have captured these delivery systems - along with sarin gas - from government armouries is unknown. Even if they have, experts said that operating these weapons successfully would be exceptionally difficult.
The investigators had enough evidence to trace the trajectories followed by two of the five rockets.
If the data they provide is enough to pinpoint the locations from which the weapons were launched, this should help to settle the question of responsibility.
John Kerry, the US Secretary of State, says the rockets were fired from areas of Damascus under the regime's control, a claim that strongly implicates Assad's forces.