Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un, was killed on February 13 after two women approached him at Kuala Lumpur International Airport and wiped a toxic substance on his face. He sought help from airport staff, suffered convulsions and died on the way to hospital. He had been waiting for a flight to Macau, where he lived with his family, and was travelling on a passport bearing the name Kim Chol.

Malaysia’s police chief said preliminary toxicology tests found VX nerve agent on swabs from Kim’s eyes and face. VX is a highly potent chemical warfare agent banned under the 1993 Chemical Weapons Convention. It can be absorbed through the skin, eyes, lungs or digestive system, and even a small amount can be fatal. Its oily consistency also makes it persistent, raising concerns about contamination at the airport and places where Kim received medical care. Authorities said they would decontaminate areas visited by the suspects; no passengers, airport workers or medical staff were reported to have fallen ill.

Malaysian investigators said two women, one Vietnamese and one Indonesian, applied chemicals to Kim’s face. Police said one woman was aware she was handling a toxin and that one of the women later suffered vomiting. Relatives and acquaintances of the suspects insisted the women may have been deceived. Investigators also detained a North Korean and sought several other North Koreans, including an embassy official and an airline employee. Police were investigating how VX entered Malaysia.

The killing triggered a diplomatic dispute and widespread suspicion of North Korean involvement. North Korea denied responsibility, accused Malaysia of fabricating evidence and blamed it for the death of a North Korean citizen. Pyongyang did not acknowledge that the dead man was Kim Jong-nam and objected to Malaysia’s post-mortem examination. Malaysia warned that the North Korean ambassador could be expelled over his statements.

Kim Jong-nam was the eldest son of former leader Kim Jong-il and had once been considered a potential successor. He later lived abroad and criticized North Korea’s policies and dynastic succession. North Korea has not signed the chemical weapons convention and is believed to possess a substantial arsenal that includes nerve agents. Estimates cited in the reports put its chemical weapons stockpile at between 2,500 and 5,000 metric tons.