Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un, died after an attack at Kuala Lumpur International Airport on February 13. Malaysian authorities said toxicology tests found VX nerve agent on his face and eyes. He sought medical help after two women allegedly wiped a substance on his face, then suffered convulsions and died on the way to hospital. He was travelling under the name Kim Chol and was reportedly waiting for a flight to Macau, where he lived with his family.

Malaysian investigators suspect North Korean agents directed the attack. Two women, one Vietnamese and one Indonesian, were detained, and police sought several North Koreans, including an embassy official and an airline employee. Relatives and acquaintances of the women said they believed the suspects had been duped, while Malaysia’s police chief said one woman knew she was handling a toxin. Police also said the women had suffered vomiting. Investigators were examining how VX entered Malaysia.

North Korea denied responsibility, accused Malaysia of fabricating evidence and blamed it for the death of a North Korean citizen. It did not acknowledge that the deceased was Kim Jong-nam. The dispute strained relations between the countries, and Malaysia warned that it could expel the North Korean ambassador over his accusations.

VX is a highly toxic, persistent nerve agent banned under the Chemical Weapons Convention, which North Korea has not signed. It can be absorbed through the skin and disrupts nerve signals; a small quantity can be fatal. Its discovery raised public safety concerns because the airport had gone 11 days without decontamination. Authorities said they planned to clean areas visited by the suspects. No passengers, airport workers or medical staff who treated Kim were reported to have fallen ill.

North Korea is believed to possess a large chemical weapons stockpile, estimated by South Korea’s defense ministry at 2,500 to 5,000 tonnes, including VX. Kim Jong-nam, once considered a possible successor to his father, Kim Jong-il, had lived abroad after falling out of favor and had criticized North Korea’s dynastic succession and policies.