He and Dr Ingrid Karnstein were sent to Haiti in 1915, ostensibly to do research on the use of tetrodotoxin and datura to slow the bleeding of injured soldiers. However, that was a cover for the real purpose, to create mindless zombies with a high immunity to damage in use in combat, as well as the use of such drugs for mind control.
When the government fell and American troops invaded, Karnstein took advantage of the chaos to destroy her notes and as much of the laboratory where the research had been done. Von Stein argued with her when he discovered what she had done. She kneed him in the groin and ran away. Due to a gas leak caused by the damage, the laboratory shortly thereafter exploded, killing von Stein. (PROSE: White Darkness)