A liter of the nerve agent VX contains enough lethal doses, theoretically, to kill 1 million people. A small drop on the skin can kill a grown man. It has no other purpose than being an instrument of death. This is one reason most of the world has banned what is truly a weapon of mass destruction.

This is also one reason it is so monstrous that North Korean leader Kim Jong Un and his coterie of brutalists may have used VX to murder his half brother Kim Jong Nam.

The assassination is reminiscent of how former KGB officer and dissident Alexander Litvinenko was silenced in London with radioactive polonium put into his tea. A British investigation found that the Russian security service and President Vladimir Putin “probably approved” it, although there was no direct proof, just a telltale radioactive trace left by the Russians who carried it out. In the same way, the killing of Kim Jong Nam seems likely to be the result of Kim Jong Un’s orders.

North Korea is one of the few nations that have not signed the Chemical Weapons Convention, which bans VX. Aside from the bucking of international norms, the assassination underlines grave questions about how Kim might behave in moments of crisis with the regime’s nuclear weapons. He is impetuous, irrational, bullying and armed.

North Korea ought to be placed back on the U.S. list of nations that sponsor terrorism, from which it was removed almost a decade ago. China recently curtailed coal imports from North Korea, but sanctions could be intensified still further against Pyongyang’s financial system and the Chinese companies that do business there. There must be no ambiguity in the message from the United States and its allies: This was outlaw behavior.