Syria 21 August attack: Frank Gardner on what we know
31 August 2013 Last updated at 01:13 BST
As governments wrestle with how to respond to Syria's alleged use of chemical weapons against its own people, the debate continues over exactly what happened and who was responsible for the deaths of hundreds of Syrians in the early hours of 21 August.
The West says the regime used nerve gas, Syria says it was the rebels, and Russia says there is no proof either way.
The BBC's security correspondent, Frank Gardner, has been examining the evidence and has compiled this special report on what happened that morning.
This report contains some graphic images that you may find distressing.