Brother of Kim Jong-un was killed with toxic substance in 2017 but women involved say they were unwitting participants.

A Malaysian judge has ruled that two women accused of participating in the assassination of the North Korean leader’s estranged brother must mount a defence, setting the stage for a lengthy case, which could last for several more months.

The proceedings on Thursday could have ended with the court ordering the release of 25-year-old Indonesian citizen, Siti Aisyah, and Vietnamese national Doan Thi Huong, who is 28.

They are accused of killing Kim Jong-nam by smearing a toxic agent, known as VX, on his face while he was at Kuala Lumpur’s airport on February 13, 2017.

The women say that they thought they were taking part in a prank for a reality TV show. Defence lawyers said the real culprits had left the country at a hearing last year.

South Korean and US officials have said Kim Jong-un‘s leadership was behind the death. North Korea denies the allegation.

Siti Aisyah is brought into court by Malaysian police officers. [Lai Seng Sin/Reuters]

High Court Judge Azmi Ariffin said it can be inferred from evidence presented in court that there was a “well-planned conspiracy” between the two women and four North Korean suspects at large to kill Kim “systemically.”

He said he “cannot rule out that this could be a political assassination” but noted there was no concrete evidence to support this.

The judge the prosecution during the six-month trial so far had laid out enough evidence of the women’s guilt for the case against them to proceed.

“I, therefore, call upon them to enter their defence,” the judge said after reading his ruling for more than two hours.

The two young Southeast Asian women are the only suspects in custody and face the death penalty if convicted. The four North Korean suspects fled the country the same morning Kim was killed.

Kim Jong-nam fell out of favour with the North Korean leadership in 2001 [Kyodo/Reuters]

Kim, who was 45 or 46, was the eldest son of the family that has ruled North Korea since its founding, yet he reportedly fell out of favour in 2001 when he was caught trying to enter Japan on a false passport, saying he wanted to visit Tokyo Disneyland.

Indonesia’s ambassador to Malaysia says he was shocked by a judge’s ruling that evidence presented so far warranted continuing the murder trial of an Indonesian suspect in the assassination of the North Korean leader’s half-brother.

Ambassador Rusdi Kirana told reporters that his government will abide by the ruling.