Two women are set to go on trial over the Cold War-style execution of Kim Jong-un's half-brother in one of the world's most high-profile murder mysteries.

Kim Jong-nam, 45, died an agonising death on February 13 as he waited to board a plane to Macau at Kuala Lumpur airport.

He was killed using the highly toxic liquid nerve agent VX - a chemical compound so deadly it is classified by the United Nations as a weapon of mass destruction.

Read more: Kim Jong Nam's accused killers plead not guilty

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Malaysian authorities described the killing as a brazen, public assassination that happened in a crowded airport.

The brutal crime captivated global media attention and was clearly meant to send a message.

A South Korean spy agency initially said the death was part of the North Korean leader Kim Jong-un's five-year plot.

Kim Jong Nam was poisoned in February. Photo / AP
Kim Jong Nam was poisoned in February. Photo / AP

A Korea University professor investigating the assassination - and who previously led a research arm with South Korea's intelligence agency - recently told GQ it was all "part of a master plan."

"Pyongyang wanted to send a worldwide message by murdering Kim Jong-nam in this gruesome, public way," Prof. Nam Sung-wook said.

"Pyongyang wanted to horrify the rest of the world by releasing a chemical weapon at an airport."

Whatever the reason for his death, Kim Jong-nam's murder sparked a fierce row between North Korea and Malaysia. Both countries expelled each other's ambassadors amid global alarm over the rogue nation's atomic weapons programme.

The North has denied the allegations. Instead, it suggested Kim died of a heart attack and accused Malaysia of working with South Korean and other "hostile forces" in blaming Pyongyang.

The women charged

Two women from humble backgrounds in Indonesia and Vietnam are accused of rubbing toxic VX nerve agent in Kim Jong-nam's face. Siti Aisyah and Doan Thi Huong, both in their 20s, will face court over the charges.

Hung is now referred to as the "LOL assassin" after security footage appeared to show her lunging at Kim while dressed in a T-shirt emblazoned in big black letters, LOL, an acronym for laughing out loud.

Doan Thi Huong has become known as the LOL assassin after security camera footage went viral. Photo / News Corp Australia
Doan Thi Huong has become known as the LOL assassin after security camera footage went viral. Photo / News Corp Australia

Malaysian police have also suggested the women were pawns in a North Korean plot to murder Kim, who was dead within 20 minutes of the attack.

The pair claim they were duped into believing they were taking part in a prank for a reality TV show have pleaded not guilty.

Defence lawyers said the real culprits have left Malaysia and that the women's innocence will be proven in court.

Alleged assassin Doan Thi Huong. Photo / Facebook
Alleged assassin Doan Thi Huong. Photo / Facebook

"We are fairly confident that at the end of trial, they will probably be acquitted," Hisyam Teh Poh Teik, a lawyer for Huong, told AFP.

Their only appearances since February have been at heavily guarded court dates, with the pair dwarfed by heavily armed police as they have been ushered into hearings wearing flak jackets and handcuffs in front of the world's media.

Suspects Siti Aisyah (left) and Doan Thi Huong. Photo / AP
Suspects Siti Aisyah (left) and Doan Thi Huong. Photo / AP

The women are the only suspects in custody in a killing. Police say several North Koreans suspected of involvement left the country on the day of the attack and others were allowed to leave later in a diplomatic deal with Pyongyang. The women will face the death penalty if convicted.

The closely-watched trial is due to begin at 10am local time (1pm AEDT) in Malaysia's High Court, just outside Kuala Lumpur, with the prosecution to start presenting its case after the women's pleas. It is expected to last for about two months, after which the judge will decide if there is a strong case for the women to have to mount their defence.

What Kim was doing before he died

Kim Jong-nam was the firstborn, illegitimate son of former leader Kim Jong Il, yet he reportedly fell out of favor in 2001 when he was caught trying to enter Japan on a false passport, saying he wanted to visit Tokyo Disneyland.

He had been living abroad for years and at the time of his death was travelling on a North Korean diplomatic passport under the name "Kim Chol."

Regardless of his reasons for visiting Japan, the scandal was nonetheless an embarrassment that revealed to the world that North Koreans travelled using fake passports, according to CNN.

North Korean leader Kim Jong-un. Photo / AP
North Korean leader Kim Jong-un. Photo / AP

North Korea has a long history of ordering killings of people it views as threats to its regime, though Kim was not thought to be seeking influence over his younger brother.

The pair are not believed to have ever met.

Kim had, however, spoken out publicly against his family's dynastic control of the reclusive, nuclear-armed nation.

Until his death, Kim lived a lavish but subdued lifestyle, fearful of a younger brother who analysts say would always see him as a threat, analysts told CNN.