A chemical attack on the town of Douma killed 43 people in 2018. Now Assad has fallen, the enforced silence of those who witnessed it is over

For years, residents of Ghouta, an embattled opposition-held region on the outskirts of Damascus, grew used to death loudly announcing its presence. When Syrian and Russian jets or helicopter gunships roared overhead, bombs were never far behind. But the night of 7 April 2018 was different.

According to an extensive investigation by the Organisation for the Prohibition of Chemical Weapons (OPCW), two yellow cylinders were dropped from a Syrian air force helicopter, crashing through the top floor of one apartment building and landing on a balcony of another, in the eastern Ghouta town of Douma. The noise they made was negligible compared with the explosions of barrel bombs and airstrikes. But the concentrated green-yellow chlorine gas that hissed out of the canisters was no less deadly.