A North Korean royalty, two female assassins and a poison-laced weapon.
The dramatic assassination of Mr Kim Jong Nam, North Korean leader Kim Jong Un's estranged half-brother, sounds like something straight out of the pages of a spy novel.
Here's a look at some of the theories and questions surrounding his sudden death at the Kuala Lumpur airport.
1. WHY HIM?
He was still considered a threat, even though he had been living in exile for more than a decade.
"Maybe Kim Jong Nam was about to do something drastic that would either compromise the regime or the family," said Dr Jae H. Ku, director of the US-Korea Institute at the Johns Hopkins School of Advanced International Studies. "By the nature of things in North Korea, the fact that he is in the bloodline represented a threat."
Some political commentators believed that the Chinese government was keeping Mr Kim Jong Nam as a reserve, so that Beijing has the option of helping him assume power should his younger half-brother fail.
He was said to be close to his uncle Jang Song Thaek, who was North Korea's second most powerful man until he was executed on Mr Kim Jong Un's orders in 2013. Jang, known to be close to Beijing and an advocate of economic reform in North Korea, was charged with treason.
The late Kim is also believed to have links to Beijing's elite.
He and Jang were probably too close to China for Mr Kim Jong Un's comfort. The latter, who came to power after the death of his father Kim Jong Il in 2011, has yet to even meet Chinese President Xi Jinping. He has angered Beijing with his provocative weapons and missile tests.
Theory 2: Too critical of the regime
He had been publicly critical of the transfer of power that made his younger half-brother the top leader after the death of their father.
He had said that his father was against a third-generation succession of power, but named Mr Kim Jong Un as the next leader to ensure national stability.
"I believe that my father originally was against the notion of a third generation succeeding him," he told Japanese journalist Yoji Gomi in an interview in November 2010. "There must have been some internal reasons that made him change his mind."
He had also once predicted failure for Mr Kim Jong Un's rule while talking to Japanese journalists.
The apparent murder "is the latest explosive turn in Pyongyang's vicious palace intrigue", said Dr Nicholas Eberstadt, a political economist who specialises in North and South Korea at the American Enterprise Institute in Washington.
"The question remains: Do these deadly measures secure his rule or serve to undermine it?" Dr Eberstadt added.
Theory 3: Display of Kim Jong Un's power, egged on by his loyalists
Since taking power, the North Korean leader has executed more than 140 senior party and military officials deemed a threat to his authority, according to the Institute for National Security Strategy, a research group affiliated with the South's National Intelligence Service.
The assassination might also have been a warning to all North Korean expatriates, said Mr Ken E. Gause, a specialist in leadership studies at the CNA Corporation, a research group in Virginia. "Given the recent defections," he said, "Kim Jong Un felt the need to show that the regime could get to anyone who may be contemplating opposing the regime."
The killing was also likely motivated by a recent news report that Mr Kim Jong Nam had sought to defect to the European Union, the United States or South Korea as early as in 2012.
Moreover, Mr Kim Jong Un has reportedly had a "standing order" to kill his half-brother since he took power in 2011, which reflected the former's paranoia.
Pundits told Korea Herald that some fervent subordinates of the North Korean leader, in their bid to show their loyalty to him, might have acted on a tacit order to take out Mr Kim Jong Nam. It is said no one would have dared to carry out the act without leader leader Kim's approval.
2. WHAT IS THE MURDER WEAPON?
Was it a poison-tipped pen or poisoned needles? Or perhaps a chemical spray or cloth soaked in poison?
Early reports have said it was death by poisoned needles. But some other reports later said he was smothered or sprayed with something poisonous.
Liquid poison is likely used, according to reports. The type of poison has yet to be determined, but one Malaysian police officer said it is "more potent than cyanide".
Cyanide is said to be the fastest killer and the easiest to detect, as its pathology appears all over the body.
Other possible chemicals include:
- Ricin which is found in castor oil plant seeds
- Thallium or rat poison
- Arsenic which delivers a slow and miserable death
- Strychnine which induces extreme body spasms as the victim's respiratory system collapses
- Excess potassium can also lead to a heart attack very quickly
- A toxic pen containing neostigmine bromide in its tip can kill a victim in three seconds with only as little as 10mg.
3. WHO ARE THE ASSASSINS?
Malaysian police arrested a fourth suspect on Friday (Feb 17). The 47-year-old suspect was found to be holding a North Korean passport at the time of arrest. The first arrest was made on Wednesday (Feb 15) when police detained a woman holding Vietnam travel papers and said they are looking for a "few" other foreign suspects in connection with the murder.
Since then Indonesian Siti Aisyah was arrested at a hotel in Ampang. Police said she was identified based on CCTV footage at the airport and was alone at the time of arrest. Her boyfriend was also picked up by police to assist with investigations.
South Korea's spy agency has said it suspected two female North Korean agents had murdered Mr Kim, while US government sources also said they believed North Korean assassins were responsible.
The woman detained at Kuala Lumpur airport was identified from CCTV footage at the airport and was alone when she was caught. Media had earlier published a grainy CCTV-captured image of a young woman wearing a white T-shirt with the letters "LOL".
Twitter was abuzz earlier over a tweet by ABC News' Seoul Bureau Chief Joohee Cho claiming that Malaysian police had found the bodies of two women believed to be operatives.
4. WHY IN MALAYSIA?
Over the past years, Mr Kim has made frequent appearances in Kuala Lumpur, triggering rumours he had moved to Malaysia around 2012.
He was fatally attacked on Monday (Feb 13) with poison by two women at the Kuala Lumpur International Airport 2 (KLIA2) while waiting for a flight to Macau. He was reported to have entered Malaysia from Macau on Feb 6.
Observers have suggested that Malaysia may have been a good hideout for him.It is one of the few countries that have good ties with North Korea, which is facing tightening global sanctions over its nuclear tests and ballistic missile launches. Pyongyang on Sunday (Feb 12) just launched a ballistic missile.
Malaysia has also often been considered an ideal spot for North Korea's espionage, according to ranking officials familiar with inter-Korea affairs.
But perhaps more significantly, he is believed to be protected by Beijing when he was in Macau, where he spent a large part of his time, and it would have been more difficult to carry out the killing there.
5. WHAT WILL HAPPEN TO HIS FAMILY?
He had been living, under Beijing's protection, with his second wife in the Chinese territory of Macau, according to South Korea's spy agency. They have a son and a daughter.
But the South China Morning Post reported that Mr Kim was rarely seen with his family, who live in a villa tucked away in a wooded part of Macau's outer island Coloane.
Mr Kim himself preferred to stay at the Mandarin Oriental near the Macau ferry terminal.
He also had a wife and son in Beijing.
The safety of Mr Kim Han Sol, 21, the son he had with his second wife, is now one of the concerns raised by some. He had previously been critical of his uncle Kim Jong Un.
Mr Kim Han Sol, who once studied in Bosnia and later in France, said in an interview with a European television channel in 2012, that he did not know how his uncle Kim Jong Un "became a dictator", when asked why his uncle was appointed as leader.
"My dad was definitely not really interested in politics. I really don't know how he (Kim Jong Un) became a dictator ... It was between him and my grandfather," he said.
6. WHAT NEXT?
On Friday (Feb 17), Kang Chol, North Korea's ambassador to Malaysia, made the first official remarks from Pyongyang when he accused Malaysia of colluding with "hostile forces", and added any results of a post-mortem examination carried out by Kuala Lumpur on the body will be rejected.
In Pyongyang, celebrations began on Thursday (Feb 16) to mark the anniversary of the birth of Dear Leader Kim Jong Il, with no announcement of the killing by the North's official Korean Central News Agency (KCNA).
The vast majority of the people in North Korea would have been oblivious to Monday's killing.
China's Foreign Ministry said on Wednesday (Feb 15) that it was closely watching developments following the incident.
In South Korea, presidential hopefuls from ruling and opposition parties united in condemning North Korea.
Mr Moon Jae In, the main opposition Democratic Party's candidate and the race's front runner, said, "North Korea is not a normal country... We should always roll out inter-Korean policies considering that it is an unpredictable counterpart".
In the United States, the Trump administration, which already faces a stiff challenge from a defiant North Korea over its nuclear arms programme and the test of a ballistic missile last weekend, may relist the North as a state sponsor of terrorism, some analysts said.
Sources: NEW YORK TIMES, YONHAP, KOREA HERALD/ASIA NEWS NETWORK, THE STAR/ASIA NEWS NETWORK, AFP, REUTERS, SOUTH CHINA MORNING POST