Four days after the killing, many questions remain unanswered. Here's what we know so far.

What happened?

Kim was on his way to catch a flight Monday morning to see his family in Macau, where he's lived since his departure from North Korea years ago.

The Chinese territory, a short ferry or helicopter ride from Hong Kong, is a popular gambling destination with mainland Chinese.

The exact details of Kim's murder are sketchy but Selangor State Criminal Investigations Department Chief Fadzil Ahmat told Reuters Kim "felt like someone grabbed or held his face from behind."

Kim felt dizzy and immediately went to an airport customer assistance counter, seeking medical help. They were concerned enough to take him to the on-premises clinic.

An ambulance was called to take Kim to the hospital, but he died on the way.

How was he killed?

No one is exactly sure how Kim died.

Initially, local media put forth reports of poison needles and deadly sprays, but it wasn't even clear whether Kim was killed or had a heart attack.

Then on Wednesday, South Korea's Lee Cheol Woo, the chairman of the country's National Assembly Intelligence Committee, publicly declared Kim had been murdered.

The autopsy may have revealed more, but despite having been finished on Wednesday, no results have been released.

As of yet, Deputy Prime Minister Hamidi said no next of kin had come forward to claim the body.

Was North Korea involved?

No motive for the killing has been revealed, nor any explanation of how he was poisoned.

South Korea's Lee told lawmakers on Wednesday that North Korea killed Kim but, again, he didn't explain how he knew it.

"Pyongyang has been attempting to assassinate Kim Jong Nam for the past five years," a South Korean legislator, Lee Chul Woo, told reporters Wednesday. He didn't provide any evidence.

When asked about rumors that North Korea had been involved in Kim's death, Malaysian Deputy Prime Minister Ahmad Zahid Hamidi told a press conference Thursday it was "only speculation."

North Korea has requested Kim's body, but Malaysian authorities said they wouldn't release it until investigations are complete. The North Korean ambassador's statement said Malaysia initially told consular officials that Kim died of a heart attack on the way to a hospital.

North Korea accused Malaysia of "collusion with the hostile forces towards our government."

Who did it?

Grainy security video from the airport at the time of Kim's killing showed two young female suspects. One of the women is seen wearing a blue skirt and white t-shirt with "LOL" written on it.

The first woman was arrested on Wednesday morning at Kuala Lumpur International Airport, two days after the attack. She was carrying Vietnamese documents, which said her name was Doan Thi Huong and gave her age as 30.

Later that evening, 26-year-old Malaysian Muhammad Farid Bin Jalaluddin was taken into custody. Police said he was arrested to assist in their investigations.

At 2 a.m. on Thursday, Jalaluddin led investigators to his girlfriend, 25-year-old Indonesian Siti Aishah, who was then arrested on suspicion of being involved in Kim's death. No charges have been laid.

Who was Kim Jong Nam?

Born in 1971, he was the first son of then-North Korean leader Kim Jong Il.

His mother was one of the dictator's favored mistresses, actress Song Hye-rim, and for a while Kim Jong Nam was the most public of his father's sons.

But in 2001 he reportedly lost the elder Kim's favor when he tried to use forged documents to visit Tokyo Disneyland.

His half-brother, Kim Jong Un, was born to a different mistress, Ko Yong Hui, who was politically ambitious and enthusiastic to see her son succeed his father as leader.

But author Yoji Gomi, who wrote a book in 2012 called "My Father, Kim Jong Il, and Me" said Kim Jong Nam thought his younger brother wasn't fit to run the country.