Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un, died after being attacked with the banned nerve agent VX at Kuala Lumpur’s airport, Malaysian police said. Toxicology tests detected the substance in swabs from his face and eyes. The killing has prompted an investigation and a diplomatic dispute between Malaysia and North Korea.

On February 13, two women approached Kim in the airport check-in area and allegedly wiped chemicals on his face. He sought medical help, suffered convulsions and died on the way to a hospital. Malaysian authorities said one of the women later experienced vomiting and that the suspects had washed their hands after the attack. Relatives and acquaintances of the women have said they believe the pair were duped; authorities dispute that account. Police detained suspects and sought several North Koreans for questioning, including an embassy official and an employee of the state airline.

VX is an exceptionally potent nerve agent that can kill in small quantities through skin contact. It is banned under the Chemical Weapons Convention, which North Korea has not signed. Its oily consistency means it can remain dangerous for an extended period, raising concerns about contamination at the airport and potentially in medical facilities or the ambulance used to transport Kim. Malaysian authorities said they were arranging to decontaminate areas visited by the suspects. No passengers, airport workers or medical personnel who treated Kim had reportedly fallen ill.

Malaysia has alleged that North Korean agents carried out the attack. Pyongyang denied responsibility, criticized Malaysia’s investigation and post-mortem examination, and accused Malaysian authorities of acting under South Korean influence. It blamed Malaysia for the death of a North Korean citizen and did not acknowledge that the victim, who was travelling under the name Kim Chol, was Kim Jong-nam. The dispute strained relations between the countries, which had previously maintained relatively accessible travel and business ties.

Kim Jong-nam, the eldest son of former leader Kim Jong-il, had once been considered a possible successor but lived abroad for years and became a critic of North Korea’s dynastic succession and policies. Experts believe North Korea holds a substantial chemical weapons stockpile and has the capacity to produce large quantities of such agents. The killing also recalled the use of homemade VX by Japan’s Aum Shinrikyo cult in attacks in 1994 and 1995, one of which was fatal.