Malaysian authorities say Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un, was killed with the banned VX nerve agent at Kuala Lumpur’s airport on February 13. Preliminary toxicology tests detected VX on his face and eyes after two women approached him in the check-in hall. Kim sought help from airport staff, suffered convulsions and died on the way to hospital. He had been travelling under the name Kim Chol.

Malaysian investigators say the women applied chemicals to Kim’s face while North Korean agents observed. One of the women later suffered vomiting, police said. Authorities were investigating how VX entered Malaysia and seeking several North Koreans, including an embassy official and an airline employee. Relatives and acquaintances of the women said they believed the suspects had been deceived; Malaysian police maintained that at least one woman knew she was handling a toxin.

VX is a highly toxic, persistent nerve agent that can enter the body through the skin, eyes, lungs or digestive system. Even a tiny amount can be fatal. Its discovery raised questions about possible contamination at the airport and places Kim or the suspects visited. Police said decontamination was underway, after the airport had remained untreated for 11 days. No passengers, airport workers or medical staff were reported to have fallen ill.

The killing triggered a diplomatic dispute between Malaysia and North Korea. Pyongyang denied responsibility, accused Malaysia of fabricating evidence under South Korean influence and said Malaysia bore responsibility because the death occurred on its soil. North Korea also declined to confirm that the dead man was Kim Jong-nam and objected to Malaysia’s post-mortem examination. Malaysia warned the North Korean envoy against making false allegations.

Kim Jong-nam, the eldest son of former leader Kim Jong-il, had once been considered a potential successor but lived abroad for years and became a critic of North Korea’s leadership and dynastic succession. North Korea has not signed the Chemical Weapons Convention. Outside estimates put its chemical weapons stockpile at 2,500 to 5,000 tonnes, with VX believed to be among the agents held.