Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un, was killed at Kuala Lumpur International Airport on February 13 after two women approached him and wiped a substance on his face. He sought help from airport staff, suffered convulsions and died on the way to hospital. Malaysian police said preliminary tests found the banned VX nerve agent on swabs from his face and eyes.

Kim, the eldest son of former North Korean leader Kim Jong-il, had once been considered a possible successor to his father. He had lived abroad for years, most recently in Macau, and had criticized North Korea’s dynastic succession and policies. He was traveling on a passport under the name Kim Chol. North Korea acknowledged that a citizen had died but did not identify him as Kim Jong-nam.

Malaysian authorities accused North Korean agents of organizing the attack and detained suspects including the two women, one Vietnamese and one Indonesian. Police also sought several North Koreans, including an embassy official and an employee of the state airline Air Koryo. Relatives and acquaintances of the women said they believed the pair had been deceived. Police maintained that the women knew they were handling a toxin, pointing in part to their washing their hands afterward. One woman reportedly vomited after the attack.

The discovery of VX raised questions about how the attackers handled the substance and how it entered Malaysia. VX is a highly toxic, persistent nerve agent that can be absorbed through the skin and can kill in very small quantities. It is banned under the Chemical Weapons Convention, which North Korea has not signed. Authorities began decontaminating areas of the airport visited by the suspects approximately 11 days after the attack. No passengers, airport workers or medical staff who treated Kim were reported to have fallen ill.

North Korea denied involvement and accused Malaysia of conducting a flawed investigation under the influence of its enemies. A North Korean statement placed responsibility for the death on Malaysia because it occurred there, while invoking North Korea’s status as a nuclear-armed state. The killing and dispute over Kim’s body strained relations between the two countries; Malaysia warned that the North Korean ambassador could be expelled over his statements.

The case also renewed attention to North Korea’s chemical weapons capabilities. Estimates cited in the reports placed its stockpile at 2,500 to 5,000 metric tons and its potential annual production at up to 4,500 metric tons in a typical year, rising to 12,000 during an extended crisis. North Korea is believed to possess several chemical agents, including VX. The passages also recalled that Japan’s Aum Shinrikyo cult used homemade VX against three people in 1994 and 1995, killing one.