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. Kim sought help after two women approached him and applied a substance to his face; he suffered convulsions and died on the way to hospital.

VX is a highly toxic, persistent chemical warfare agent that can be absorbed through the skin. Even a small amount can be fatal. Its use is banned under the Chemical Weapons Convention, which North Korea has not signed. The discovery raised questions about how the substance entered Malaysia and whether the airport, medical facilities or ambulance had been contaminated. Authorities began decontaminating areas of the airport after it had remained open for days following the attack. No passengers, airport workers or medical staff were reported ill.

Malaysian police detained two women, one Vietnamese and one Indonesian, and sought several North Koreans for questioning, including an embassy official and an airline employee. Police said at least one woman knew she was handling a toxin, while relatives and acquaintances maintained that the women had been deceived. Authorities also said the women had been instructed to wash their hands after the attack; reports differed on the extent to which they became ill.

The killing triggered a diplomatic dispute. Malaysia’s investigation pointed to North Korean involvement, while Pyongyang denied responsibility, accused Malaysia of fabricating evidence and objected to the post-mortem examination. North Korea did not acknowledge that the dead man, whose passport identified him as Kim Chol, was Kim Jong-nam.

Once considered a potential successor to his father, Kim Jong-il, Kim Jong-nam had lived abroad and criticized North Korea’s leadership and dynastic succession. His death intensified scrutiny of North Korea’s reported chemical weapons program. Estimates cited in the reports put its stockpile at 2,500 to 5,000 tonnes, potentially including VX, sarin, mustard agent and phosgene.