As authorities hunt for clues in the mysterious murder of North Korean leader Kim Jong Un’s elder half brother, Kim Jong Nam — reportedly at the hands of agents from the North — ties to Japan by both brothers may figure prominently in the audacious killing.

Kim Jong Nam was killed Monday morning at Kuala Lumpur International Airport as he was readying to board a flight to the Chinese enclave of Macao, South Korean authorities confirmed Wednesday. News of his dramatic death first emerged late Tuesday.

But while South Korea’s spy agency said that it suspects the North to be behind the murder, it did not directly blame Pyongyang. According to the South’s Yonhap news agency, however, National Intelligence Service (NIS) Director Lee Byung-ho told lawmakers that for the past five years Pyongyang had been attempting to assassinate Kim Jong Nam, who had been under the Chinese government’s protection.

Lee, however, did confirm that Kim was killed with poison at the airport, likely by what Malaysian police believed were two females who carried out the attack.

Malaysian police said Wednesday that they had detained a woman holding a Vietnamese travel document in connection with the killing.

Earlier, Kyodo News, citing an anonymous Japanese government official, had reported there was information suggesting the pair might already be dead.

The two females splashed Kim’s face with what was believed to be a chemical at the airport’s departure hall at around 9 a.m. Monday, later fleeing the scene by cab, the Malaysia Star newspaper quoted police official Fadzil Ahmat as saying.

“He told the receptionist at the departure hall that someone had grabbed his face from behind and splashed some liquid on him,” Fadzil said.

“He asked for help and was immediately sent to the airport’s clinic. At this point, he was experiencing headache and was on the verge of passing out,” according to Fadzil. “At the clinic, the victim experienced a mild seizure. He was put into an ambulance and was being taken to the Putrajaya Hospital when he was pronounced dead,” he added.

Yoji Gomi, a Japanese journalist and author of the book “Kim Jong Nam: My Father, Kim Jong Il and Me,” which is based on more than 150 email exchanges and seven hours of interviews, said that he was deeply troubled by the killing of Kim, who he called a friend and who appeared uninterested in seizing power.

“I thought I would have the opportunity to meet him again,” Gomi, a senior staff writer at the Tokyo Shimbun, told The Japan Times. “I am sure he had things he wanted to say.”

The eldest son and onetime heir apparent to late former North Korean leader Kim Jong Il, Jong Nam fell out of favor with his father after he was caught in an embarrassing bid to enter Japan on a false passport in 2001 in order to visit Tokyo Disneyland.

Jong Nam had long lived abroad since the incident, routinely traveling between Beijing, Macao, Singapore and Kuala Lumpur.

“It has been some time since he was ousted from the power structure of the North Korean regime, but he is the only one who can criticize the regime as a member of the Kim family,” Gomi said. “I was hoping that he would have brought unexpected changes.”

Still, Jong Nam, a rotund and jovial figure, had been one of the very few members of the Kim family to criticize the regime — and live to talk about it — lambasting the dynastic approach to ruling the North that saw Kim Jong Un groomed to take power.

“Personally, I am against third-generation succession,” Jong Nam told Asahi TV in 2010. “I hope my younger brother will do his best for the sake of North Koreans’ prosperous lives.”

This stance was unlikely to have endeared the elder brother to his sibling, who has viciously stamped out perceived threats to his power, including orchestrating the execution of his powerful uncle, Jang Song Thaek, in 2013. Jang was thought to have been close to Jong Nam.

“This assassination could signal that Kim Jong Un has moved into the final phase of his power consolidation process,” said Ken Gause, a senior analyst at the CNA think tank in Washington who has studied the North’s leadership.

“He may be going after critical networks that helped him secure power, namely the Kim Kyong Hui network,” Gause said in reference to Jang’s widow and aunt of Kim Jong Un.

Gause said she had been Kim Jong Nam’s “protector inside the regime.” Now, he said, the North Korean leader felt confident enough to go after individuals in that network, including the country’s security chief, who was sacked last month.

Others, however, have suggested an alternative theory — that the biggest obstacle to Kim Jong Un maintaining a firm grip on power is himself.

According to Ken Kato, director of the group Human Rights in Asia, Kim Jong Un may in fact be a “traitor” to the very country he rules through his family lineage.

In 2012, Kato unearthed documents that revealed Kim Jong Un’s maternal grandfather had worked in a sewing factory that made uniforms for the wartime Japanese military in Osaka, where Kim’s mother, Ko Yong Hui, was born.

This discovery, Kato said, would make the grandfather a “collaborator” — a grouping that Kim Jong Un’s other grandfather, North Korean founder Kim Il Sung, said “must be eliminated through three generations,” potentially affecting the young leader.

“Technically, Kim Jong Un could have been defined as a traitor and could be in a labor camp,” Kato said. “So we can infer that Jong Un might have been planning on killing his elder brother as he could threaten his status.”

For his part, Gomi is skeptical that Kim Jong Un ordered the alleged assassination, saying that the young leader has his hands full dealing with growing international pressure over the North’s nuclear and missile programs.

But, he said, a lack of vigilance may have brought about his death.

“When he came to Japan, he was walking around alone,” Gomi said. “I think he was enjoying his life in places like Malaysia and Singapore, staying incognito.”

Kim had been the target of at least one earlier assassination attempt in 2012, according to the South’s spy agency, something that may have prompted Kim Jong Nam to reportedly send a letter to his half brother in 2012, by then the country’s new leader, asking him to spare his and the lives of his family, which is currently under the protection of China in Beijing.

“What’s the point of rubbing him off? Kim Jong Un reportedly has been Beijing’s favorite, which may mean one day the Chinese Communist Party may overthrow him and install Kim Jong Nam,” said Sung-Yoon Lee, an assistant professor of Korean studies at the Fletcher School of Law and Diplomacy at Tufts University in Massachusetts.

According to Lee, the younger Kim “has a serious legitimacy problem in terms of his bloodline.”

“His mother, Ko Yong Hui, who was a dancer, was born in Japan,” he said. “Kim himself probably was born in Vienna or Geneva while Ko was living abroad. The Japanese bloodline has serious negative implications for the Korean ‘Sun God.’ “

More to the point, said Lee, the killing sends a chilling message to all would-be challengers.

“Don’t you dare. Disobey, and this is your grim fate,” he said.