Though American laboratories stopped producing nerve agents around 1970, after the production of so-called third-generation nerve agents like sarin and VX, Soviet scientists continued their work for two decades, producing a “fourth generation.”

The Novichok nerve agents came in solid form, like a powder or thick paste, and would not register on the chemical detector paper that NATO troops used.

A chemist who worked in the laboratory developing Novichok accidentally inhaled fumes while filling a syringe, and collapsed. Though he was injected with an antidote and eventually awoke, he suffered from depression and epilepsy and died five years later, leaving Vil Mirzayanov, a scientist who helped develop the agent, deeply disillusioned.