The cloud that brought such devastation to the Syrian town of Khan Sheikhoun had no smell and affected even those who came into contact with the dead, indicating it was sarin gas - a chemical compound developed by the Nazis and 26 times more deadly than cyanide.
Medical charity Medicins Sans Frontieres said its doctors treated victims with dilated pupils, muscle spasms and involuntary defecation - symptoms "consistent with exposure to neuro-toxic agents such as sarin," according to Daily Mail.
The World Health Organisation said the victims appeared to have been exposed to a "nerve agent".
The symptoms all point to sarin - the chemical weapon accidentally created in 1938 by German scientists working on insecticides.
The chemist in charge of the project initially thought he had failed, because the compound he had created was too deadly to animal and human life to use in agriculture. But that is exactly what appealed to Adolf Hitler, whose weapons division took over the project.
Hitler was so pleased with his new weapon, he named it "sarin" after the scientists who discovered it - Gerhard Schrader, Otto Ambros, Gerhard Ritter, and Hans-Jürgen von der Linde.
The effect of exposure to sarin gas is instant, leading to an excruciating death. Inhaling even tiny amounts causes - in less than ten seconds - drooling and vomiting, while breathing becomes shallow and erratic.
Less than a minute after exposure, the victim's nervous system is under sustained attack, making the body unable to control breathing. Lungs secrete fluid to try to repel the gas, making victims foam at the mouth with blood-flecked discharges.
Many suffer from a medical condition known as SLUDGE, which stands for Salivation, Lacrimation (tears), Urination, Defecation, Gastrointestinal distress and Emesis (vomiting). The body loses the ability to control its functions.
Many die within minutes of inhaling the gas. The maximum life expectancy is ten minutes after exposure. Those lucky enough to survive, due to receiving a much smaller exposure - such as from touching a contaminated person - often suffer permanent nerve and brain damage.
The discovery of the nerve agent - meaning it acts upon the nervous system - came after the Third Reich high command ordered scientists to develop pesticides and insecticides to ensure Germany did not need to rely on imported food while it prepared for war. Schrader, 33, headed up a team assigned to the task.
Having failed to make powerful insecticides from fluoride, he decided to mix phosphorus with cyanide. As well as killing all insects, tests on animals proved astonishing. Apes collapsed foaming at the mouth and died within seconds. Rats chewed at their skin before choking to death. Birds fell from perches without making a sound.
Yet Schrader thought he had failed in his quest because the substance could not be used in agriculture - and help feed Hitler's armies - because it was so toxic.
But Hitler immediately saw other uses for it. A keen military historian, he knew Germany had started what became known as the "chemists' war" on April 22, 1915, when chlorine gas was fired at French soldiers in the trenches.
More than 90,000 soldiers would be killed by poisonous gas, which blew in across the Allied positions as "queer greenish-yellow fog," in the words of a survivor. He added: "Many fell and died on the spot. The others, gasping, stumbling, with faces contorted, hands wildly gesticulating, and uttering hoarse cries of pain, fled madly through the villages and farms and through Ypres itself, carrying panic to the remnants of the civilian population."
The blistering agent mustard gas, or sulfur mustard, was also used by the Germans, prompting Siegfried Sassoon, the English soldier and poet, to describe the horrors of inhaling gas and the sound of "blood... gargling from froth-corrupted lungs".
Sarin is far deadlier than either chlorine or mustard gas.
So potent was this poison that in 1940, the Waffenamt - the German Army weapons agency - began building a secret production facility, staffed by scientists wearing protective suits. Schrader was brought in to head up the project.
Ten tons of sarin was produced - enough to kill millions. But Hitler never used it after being warned by his experts that the West, including Britain and America, had supplies of mustard gas and would unleash their own horrors on the Fatherland in retaliation.
Indeed, sarin was also of great interest to America and Britain. In one incident kept secret for half a century, it emerged that Britain experimented with sarin on a 20-year-old RAF engineer called Ronald Maddison at Porton Down, the secret chemical weapons research centre in Wiltshire.
In 1953, Maddison was offered three days' leave and 15 shillings for agreeing to take part in the test, which was designed to discover what effects dripping sarin on clothing had. The substance is liquid until it reaches 150 degrees C, whereupon, when fired by a shell, the explosion turns it into gas.
Maddison planned to use the money to buy an engagement ring. But after he was placed in the sealed chamber with five drops of sarin dripped on to his arm, he immediately collapsed and fell over a table.
After scientists in protective suits hauled him out, he said he couldn't breathe, hear, or see. He was taken to a hospital within the Porton Down facility, but was pronounced dead 40 minutes after being exposed.
Details emerged only when an inquest into the death was held in 2004 following years of campaigning by his family, who were also incensed by the fact the Ministry of Defence removed several of Maddison's organs, including the brain, spinal cord tissue and lungs, and used them for further experiments.
Both America and Russia also experimented with sarin gas under secret chemical weapons programmes, but never used the deadly nerve agent in operations, fearing a tit-for-tat escalation.
Infamously, Iraqi dictator Saddam Hussein used sarin against Kurds in the town of Halabja in 1998, when his war planes dropped bombs containing the nerve agent. It killed 5,000 people immediately, and a reported 12,000 in the ensuing days and months.
Then, in 1995, terrorists connected to a Japanese cult launched a sarin attack on the Tokyo underground, killing 12 people and injuring more than 5,000 - the deadliest attack on Japanese soil since the Second World War.
In an attempt to prevent the use of sarin in modern warfare, the agent was officially banned in 1997 under the United Nations chemical weapons convention. But not all stocks were destroyed.
Indeed, then US President Barack Obama claimed in 2013 that Syria had "crossed a red line" by dropping up to 1,000kg of sarin on a rebel-held area of Damascus, killing up to 1,400 people.
US military intervention was only averted when Russia brokered a deal with Syria, under which the country's president, Bashar al Assad, agreed to destroy all stockpiles of sarin and other chemical weapons.
With the world condemning the latest scenes from Syria, Russia and Assad's regime have claimed that the deaths were the result of an attack on a rebel artillery base.
The Russian defence ministry said the building housed an "arsenal of chemical weapons" intended for fighters in Iraq, and described its information as "completely reliable and objective". America and Britain seem far from convinced, and have blamed Assad.
So why would he do it? Backed by Russia, and with US policy at sea since Donald Trump's election, analysts say Assad is sending a message to rebel-held areas that he can act with impunity. Nothing, it seems, is too barbaric or sadistic for those waging war in Syria.