The declaration that the half-brother of North Korea’s dictator was killed by one of the world’s most lethal chemicals cast fresh attention on that country’s chemical and biological weapons program and the threat the country poses to the international community.

Malaysia’s police chief said Friday that the highly toxic VX agent was used in the murder of Kim Jong Nam, a disclosure that came 11 days after his death and after hundreds of thousands of travelers had passed through the busy budget terminal of Kuala Lumpur International...