From “The Invention of Modern Gas Warfare“, at Ockham’s Razor:
[Dr. Fritz] Haber [inventor of modern gas warfare] was a very patriotic German and so when the war began he looked for ways to assist the military effort. His first major critic was his childhood sweetheart and wife, Clara. She was a talented chemist herself. She was appalled at the use of science to kill people. A few days after the first use of gas, she used his army pistol to commit suicide.
This did not deter Haber. He went off to supervise the use of gas warfare on the Eastern front and he left others to handle her funeral arrangements.
When the war ended in 1918, Haber donned a disguise and fled temporarily into Switzerland. The use of gas warfare had been so controversial that he was afraid that he would be tried by the Allies as a war criminal. About 1.3 million people had been wounded by gas, with 91,000 being killed.