Three years ago in Ghouta, east of Damascus, an attack resulted in hundreds of people rushed to hospital.
They were showing symptoms consistent with sarin gas poisoning.
The effects of the chemical weapon are distressing: the chest tightens, vision blurs, and if the exposure is great enough, it can progress to convulsions, paralysis, and death ... all within 10 minutes.
A nurse working that night in the hospital spoke to the BBC.
"Most of the victims were children and babies and some mothers died immediately because they were sleeping, and by the time they realised what was happening they couldn't move."
Ghouta resident Abu Kasim says it's a war crime that's gone unpunished.
"There were 10,000 people living here. If someone was tried with murder, he'd be tried with trying to kill 10,000 people but no-one cares. It's been three years since this crime, this massacre, and no-one has paid the price for it."
The Syrian government was forced to destroy its chemical weapons stock.
But since then, there have been more attacks.
The Organisation for the Prohibition of Chemical Weapons - United Nations Joint Investigative Mechanism, known as the J-I-M, has investigated nine cases of suspected chemical weapons use.
Six were inconclusive.
But those responsible for three separate chemical weapons attacks were clear.
It's found the Syrian government responsible for using chlorine gas in two attacks, and IS fighters for using mustard gas in one attack.
French President Francois Hollande says the facts can no longer be ignored.
"There are some who do not want a peaceful solution or a political transition. We now have proof - brought by the United Nations - that the Syrian regime used chemical weapons. We knew it back in 2013 - and you know the position I took. And we also got confirmation after 2013, that's what the report says. It is also true that IS also used chemical weapons, probably similar ones to that of the regime."
The report comes as the US Secretary of State, John Kerry, and Russian Foreign Minister, Sergei Lavrov, arrived in Geneva ahead of talks focusing on the conflicts in Syria and Ukraine.
The UN's Special Envoy for Syria, Staffan de Mistura, hopes the US and Russia can begin resolving some issues.
"Those meetings that are taking place outside this office here in Geneva are going to have an impact, ertainly on the way we will be, and I plan to present, what are the political initiatives of the UN in order to relaunch the political process on Syria."
The UN is still waiting for other parties to join Russia's commitment to a weekly 48-hour humanitarian ceasefire in Syria.
Special Adviser to the UN Special Envoy for Syria, Jan Egeland, says they are ready to send supplies into Aleppo and begin critical repair work on the city's power supply.
"Initally we would be ready - in the first 48 hour weekly pause - to have two convoys of 20 trucks each that would carry enough food for 80,000 people in eastern Aleppo and, even more importantly, to have cross-line repair of the electrical system pumping water to 1.8 million people in east and in west."
For now, the bombing continues.
Two barrel bombs have been dropped in the neighbourhood of Bab al Nayra in Aleppo.
Children were pulled, limp, from the rubble.
At least five people were killed.
