What are Novichok agents and what do they do?

 Why does this point to Russia?

The agents that make Novichok were secretly developed by the former Soviet Union during the later years of the Cold War. Mirzayanov spent years testing and enhancing them before exposing the program in 1991; he was charged with treason and now lives in exile in the U.S. He says only the Kremlin knows how to make Novichok and he doubts a nonstate actor could have weaponized it.