According to information from Malaysian, South Korean and USA officials, Kim Jong Nam was poisoned in the departure hall of the airport by two North Korean female agents who fled in a taxi while he fell gravely ill and died en route to hospital.
Mark Tokola, vice president at the Korea Economic Institute in Washington, said it would be surprising if Kim Jong Nam was not killed on the orders of his brother, given that North Korean agents have reportedly tried to assassinate Kim Jong Nam in the past.
Kim Jong-nam had told airport workers that someone had attacked him "from behind" and sprayed him in the face with an unknown liquid.
Malaysian authorities denied a request by North Korean officials to turnover the body without a postmortem, according to WSJ. But why kill Kim and what threat did he pose to North Korea.
Kim Jong Nam was doomed the moment Kim Jong Un was named the future leader, the former diplomat said.
"The event explicitly showed the tragic reality of Kim Jong-un's reign of terror", explained Rep. Kim Myung-yeon, "It has increased the possibility that Kim will seek abrupt provocations against South Korea and the worldwide community to maintain his regime". Kim Jong Nam had been critical of Kim Jong Un, reportedly saying in 2012 that he "won't last long" because of his youth and inexperience.
North Korean leader Kim Jong-Un.
Kim, 46, was targeted Monday in the shopping concourse at the airport and had not gone through immigration yet for his flight to Macau, said a senior government official, who spoke on condition of anonymity because the case involves sensitive diplomacy.
US government sources have also told Reuters that they believe Jong-nam was assassinated in Kuala Lumpur and blame North Korea. But the North Korean spy agency apparently continued searching for an opening to eliminate him.
He was by-passed to become leader of North Korea when his father Kim Jong-il died, with the line of succession moving to his younger half brother. Kim Jong Nam's death may further strain that alliance.
Malaysian police investigating the attack said the cause of Kim's death was not yet known and a post-mortem would soon be carried out. Spy officials offered a single, shaky motive for the death: Kim Jong Un's "paranoia" over his estranged half brother, Associated Press reports.
"Kim Jong Un is either quite strong ... or he's feeling very vulnerable", he said.
But his attempt to visit Tokyo Disneyland reportedly soured North Korea's leadership on his potential as a successor.
Jong-Nam was an advocate of reform in the North, and once told a Japanese newspaper that he opposed his country's dynastic power transfers.