Malaysian police say they have arrested a woman in connection with the death of North Korean leader Kim Jong Un's half brother.

Wednesday's statement says the woman was arrested at Kuala Lumpur International Airport. She was carrying Vietnamese travel documents.

Kim Jong Un's half brother died Monday after suddenly falling ill at the airport. According to a Malaysian government official, Kim told medical workers before he died that he had been attacked with a chemical spray.

Who is Kim Jong Nam?

Many feared that Kim Jong Nam would be assassinated after Kim Jong Un took power in April 2012. ABC News reports a fierce rivalry between the two half-brothers ran deep because of succession conflicts. Kim Jong Nam, as the eldest son in the family, had long been expected to rule North Korea after Kim Jong Il's death and was backed by senior Communist Party members, including Jang Sung Taek.

Jang, an uncle of the two rival brothers, had been considered No. 2 in power but was brutally executed a year after Kim Jong Un took power.

"North Korea is a society where you will be easily executed not because of your difference in political reasons but because of simple reasons — that you angered Kim Jong Un," said Thae Yong Ho, a former North Korean diplomat and the highest-level North Korean official to have defected to South Korea in two decades.

"North Korean society is just the reign of terror."

Kim Jong Nam reportedly fell out of favor in Pyongyang after being caught trying to enter Japan on a fake passport in 2001. He said he was heading to Tokyo Disneyland with his family. Since then, he had been in exile, moving discreetly among several countries, such as Singapore and Malaysia, as well as Macau, Hong Kong and other parts of China. His son, Kim Han Sol, was recently enrolled at Institut d'Etudes Politiques de Paris, according to South Korean media.

The two brothers never met in person, according to North Korea analysts in Seoul. But Kim Jong Un always regarded the outspoken Kim Jong Nam as a potential political threat.

For instance, Kim Jong Un built himself up in the image of his late grandfather and the founder of North Korea, Kim Il Sung, to gain popularity and to justify his accession to power. Kim Il Sung is still revered by the people as the pillar of the nation. From the moment he began appearing in public, Kim Jong Un has emphasized striking similarities with his grandfather like gaining weight, wearing the same eyeglasses and having an identical haircut. But it was Kim Jong Nam who grew up close to their grandfather.

The fact that Kim Jong Nam was born to the first legitimate wife of Kim Jong Il took a toll on Kim Jong Un, whose mother was Kim Jong Il's third wife, Koh Yong Hee, who came from a family that defected from North Korea to Japan — which is looked down on in a country where generations of loyalty to the regime is essential.

Why was Kim Jong Nam in Macao?

The slaying of Kim Jong Nam, appears to be making few ripples so far in Macau, where he lived for years.

The Chinese gambling hub is home to a small Korean community estimated at 240 people but staff at the city's handful of Korean restaurants and shops said Wednesday they had never seen him when shown his picture.

Several said Kim was unlikely to mix with Macau's Korean residents because most were from South Korea.

Kim lived in a newer high rise building in the city's Taipa neighborhood across from a public park, according to photos published by South Korea's Yonhap news agency. A Filipino woman who lives in the building and declined to give her name said she saw him in the elevator but they never spoke.

Kim's teenage daughter attends Macau Anglican College after having transferred from an international school nearby, according to students at both schools. But none said they knew her or had seen her the day after her father's death.

Information from the Associated Press and ABC News was used in this report.

Cox Media Group