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 International Airport on February 13. Malaysian authorities said two women approached him in the check-in area and wiped a substance on his face as he waited for a flight to Macau, where he lived with his family. He sought medical help, suffered convulsions and died on the way to hospital. Preliminary toxicology tests detected VX on swabs from his eyes and face.

VX is a highly toxic, oily nerve agent that can enter the body through the skin, eyes, inhalation or ingestion. Even a small amount can be fatal, and symptoms can include vomiting, seizures and paralysis. The substance can remain dangerous on surfaces for an extended period. Its discovery raised questions about safety at the airport, where many passengers had passed through before authorities began decontamination roughly 11 days after the attack. Malaysian police said no passengers, airport workers or medical staff were reported ill.

Police detained the two women, one Vietnamese and one Indonesian, and a North Korean suspect, while seeking several other North Koreans, including an embassy official. Authorities said the women had been instructed to wash their hands after the attack; the police chief said they had suffered vomiting. Their relatives and acquaintances maintained that the women must have been deceived. Investigators were also trying to determine how VX entered Malaysia.

The killing triggered a diplomatic dispute. Malaysia suspected North Korean agents of involvement, while Pyongyang denied responsibility, criticized the investigation and blamed Malaysia for the death. North Korea did not acknowledge that the victim, who carried a passport in the name Kim Chol, was Kim Jong-nam.

Once considered a possible successor to his father, Kim Jong-il, Kim Jong-nam had lived abroad and criticized North Korea’s dynastic rule. VX is banned under the Chemical Weapons Convention, which North Korea has not signed. Estimates cited in the reports put the country’s chemical weapons stockpile at 2,500 to 5,000 metric tons.