The two women suspected of fatally poisoning Kim Jong-un's half-brother, Kim Jong-nam, were trained to coat their hands with toxic chemicals and wipe them on the man's face, according to Malaysian police.
The North Korean embassy has mocked the police's description of the attack and called for the immediate release of the two "innocent women."
"If they had toxins on their hands, how is it possible that these female suspects could still be alive?" a statement from the North Korean embassy in Kuala Lumpur read.
Surveillance footage showed the two women, Indonesian Siti Aisyah and Vietnamese Doan Thi Huong, going to the toilets at Kuala Lumpur airport to wash their hands shortly after the attack.
Police Inspector-General Khalid Abu Bakar said that the women knew they were handling toxic materials and were warned "to take precautions." He said the women had practised their attack at two shopping malls.
One of the women claimed that she was tricked into carrying out the assassination and that she believed she was taking part in a comedy prank show. Bakar dismissed the claim, commenting: "This is not just like shooting a movie."
"We strongly believe it is a planned thing and that they have been trained," he told reporters at a press conference on 22 February.
The North Korean embassy insisted however that "there is another cause of death" and said "the liquid they daubed for a joke is not a poison."
A Malaysian and North Korean man have also been arrested in connection with the attack. Police said that the North Korean suspect would be released on bail on 22 February.
Song and Kim Uk II, an employee of North Korean airline Air Koryo, are believed to have fled the country to Pyongyang. They are said to be hiding inside Pyongyang's embassy in Malaysia, security sources told The Telegraph.
Police believe the North Korean suspects supplied the two women with the toxin. "That's why we asked the North Korean Embassy to trace them and hand them over to us," Bakar said. He added that Malaysian authorities had so far received no assistance from North Korea in the investigation.