Professor Ake Sellstrom, head of the chemical weapons team working in Syria, handing over the report on the Al-Ghouta massacre to Secretary-General Ban Ki-moon. (United Nations)

Though short of a mandate to actually implicate anyone, United Nations inspectors announced this afternoon that there was “clear and convincing evidence” that chemical weapons had been used in an attack on civilians in Syria last month.

The findings represent the first official confirmation by scientific experts that chemical weapons were used in Syria’s civil war, but the report left the key question of who launched the attack unanswered.

The rebels and their U.S. and Western supporters have said the regime of President Bashar Assad was behind the Aug. 21 attack, while the Syrian government and its closest ally, Russia, blame the rebels.

The list of evidence cited in the report is as exhaustive as it is disturbing and the confirmation, coming more than three weeks after the attack, seems more a cause of histrionic breathing (or Twitter or in real life) at this point than anything else. But now we know for sure, for sure.