Kim Jong Nam, the estranged half-brother of North Korean leader Kim Jong Un, died after being attacked at Kuala Lumpur International Airport on February 13. Malaysian authorities said toxicology tests detected VX nerve agent on his face and eyes. Two women allegedly approached him in the check-in hall and wiped chemicals on his face. He sought medical help, suffered convulsions and died while being taken to a hospital. He had been travelling under the name Kim Chol and was reportedly waiting for a flight to Macau, where he lived with his family.

VX is a highly toxic nerve agent banned by the 1993 Chemical Weapons Convention. It can be absorbed through the skin, eyes, lungs or digestive system; even a small amount can be fatal. Because it is an oily, persistent substance, its discovery raised concerns about possible contamination at the airport and in the ambulance and medical facilities involved in Kim’s care. Malaysian authorities said they would decontaminate areas visited by the suspects. No passengers, airport workers or medical staff who treated Kim were reported to have fallen ill.

Malaysia detained an Indonesian woman and a Vietnamese woman in connection with the attack and sought several North Koreans, including an embassy official and an airline employee. Police said at least one of the women knew she was handling a toxin; relatives and acquaintances maintained that the women may have been deceived. Investigators said the women had been instructed to wash their hands afterward. Police also reported that they suffered vomiting, though the accounts leave uncertainty about the extent of their exposure. Experts questioned how the attackers could have handled VX and survived, suggesting that an antidote was one possible explanation.

The killing triggered a diplomatic dispute. Malaysian investigators pointed to North Korean agents, while Pyongyang denied responsibility and accused Malaysia of fabricating evidence and mishandling the investigation. North Korea had not acknowledged that the dead man was Kim Jong Nam, and Malaysia sought to question a senior member of its embassy staff. The dispute strained relations between the two countries, which had previously maintained relatively open travel ties.

Kim Jong Nam was the eldest son of former North Korean leader Kim Jong Il and had once been considered a possible successor. After being passed over in favor of Kim Jong Un, he lived abroad and criticized aspects of the North Korean regime and its hereditary succession.

North Korea has not signed the Chemical Weapons Convention and is believed to possess a substantial chemical weapons stockpile. Estimates cited in the reports placed its inventory at 2,500 to 5,000 metric tons, with VX among the agents identified. The country’s estimated production capacity was up to 4,500 metric tons in a typical year and potentially 12,000 tons during an extended crisis. The passages also noted an earlier use of homemade VX by Japan’s Aum Shinrikyo cult in attacks on three people in 1994 and 1995, one of whom died.