Chemical and biological weapons are morbidly brilliant for fighting in towns and cities, if you have no morals or scruples. And the level of psychological horror they inflict is exactly what terror groups want in their arsenal. For the past 20 years, I have been in the battle to counter the use and proliferation of these weapons. The first 10 of those years were in the military, working in the shadows to deal with toxic things in Afghanistan and Iraq. The past 10, ostensibly in Syria but really also in Iraq, I spent in a humanitarian role, trying to help unprotected civilians survive deadly fumes. As the saying goes, the only thing necessary for the triumph of evil is for good men to do nothing. In the past three years, there have been at least eight documented chemical attacks in Ghouta, Douma and Idlib province by the Syrian regime. These were predominantly carried out using chlorine, dropped as a barrel bomb or fired in a rocket. The UN’s Organisation for the Prohibition of Chemical Weapons confirmed that chlorine was used in the attack on the town of Douma, on 7 April 2018 that killed 43 people, mainly children. The regime in Damascus, the OPCW has said, is responsible. We are in the ninth year of this shockingly violent conflict. This war has become synonymous with two distinct and irrefutable crimes against humanity: the use of chemical weapons and the direct targeting of hospitals and medical personnel. In this nine-year period there have been over 200 documented uses of chemical weapons by the Syrian government and ISIS. The OPCW has been called to investigate some attacks, but Russia has used its veto power in the UN to limit its activities. I investigated a number of attacks in Syria, and on 29 April 2014, published the results of our investigation of the attacks on the Syrian towns of Kafr Zita and Talemenes a few days before. This unequivocally showed chlorine was used and the regime was responsible. The regime continued to hammer the Damascus suburbs Ghouta and Douma with chlorine barrel bombs, which have had the same effect as they did in Aleppo in December 2016. In my opinion, Syrian President Bashar Al Assad would not still be in power if he had not used chemical weapons. They are morbidly brilliant for fighting in built-up areas. Once buildings have been razed to the ground, it is almost impossible to force people out with conventional munitions. This is where gas is so effective. Mr Al Assad’s repeated use of gas has killed people underground or forced them into the open, where they are susceptible to bombs and bullets, leading to their surrender. In this era of fake news, where everything is questioned and used to distort reality, usable evidence is key. The chance to collect evidence is often fleeting and opportunistic, and it is important that medical personnel and others have a basic understanding of how to collect evidence of a chemical attack if they are in the vicinity. Too often, over the past nine years, the OPCW has either been unable to reach the sites of attacks or has been delayed to an extent that evidence has disappeared or been tampered with. At times, people have taken unbelievable risks to get evidence through Syrian Army lines to the outside world. This has been a source of great frustration for me and others in Syria over the years. In the early days, the outside world spurned it because we were not "accredited" persons from a body tasked by the international community to investigate atrocities – only for that evidence to be verified by an "accredited" body many months or years later, and too late to have an impact or bring the perpetrators to book. In more recent times, however, especially appertaining to attacks in Idlib, evidence of a standard that is admissible in an international court has found its way safely to western governments, allowing them to take direction where they saw fit. It is also forming part of a growing body of evidence that will, I hope, one day, be used by the International Criminal Court to convict those responsible for atrocities and crimes against humanity in Syria. This, for many in Syria, is the only hope driving them forward, as they continue to suffer from malnutrition, air strikes and Covid-19 in the sprawling refugee camps, with no chance that the West will come galloping over the horizon to save them. Since former US president Barack Obama's "red line" threat on chemical weapon use evaporated in the summer of 2013, these weapons have proliferated to a great extent. The apparent ambivalence from global leaders as to their use, however, cannot be allowed to deepen. With Covid-19, the world has witnessed a not very toxic biological pathogen bringing things to a standstill. Now imagine how a highly toxic biological pathogen – that could spread as rapidly as Covid-19 – could be as imposing a threat as nuclear war or climate change. We must strain every nerve and sinew to put a stop to the continued proliferation of chemical and biological weapons. <em>Hamish de Bretton-Gordon is a chemical and biological </em><em>weapons expert and </em><em>author of his memoir Chemical Warrior</em>