Two women suspected of fatally poisoning the half-brother of North Korea's leader Kim Jong Un were trained to coat their hands with toxic chemicals then wipe them on his face, Malaysian police have said.
Inspector general of police Khalid Abu Bakar also announced authorities were now seeking a North Korean diplomat in connection with the attack on Kim Jong Nam on February 13 at Kuala Lumpur's airport.
Mr Khalid told reporters authorities were searching for two new North Korean suspects, including the second secretary of North Korea's embassy in Kuala Lumpur and an employee of North Korea's state-owned airline Air Koryo.
"We hope that the Korean embassy will co-operate with us, allow us to interview them and interview them quickly," he said.
"If not, we will compel them to come to us."
Mr Khalid said the women knew they were handling poisonous materials during the attack, which occurred in a departure area of the airport, and had practised it several times.
"We strongly believe it is a planned thing and that they have been trained to do that," he said.
"This is not just like shooting a movie."
Mr Khalid could not confirm whether North Korea's government was behind the death of Mr Kim, the long-estranged half brother of North Korea's ruler, but added: "What is clear is that those involved are North Koreans."
Police have already arrested four people in connection with the attack, including the two women.
At least one of the women has claimed she was tricked into attacking Mr Kim, believing she was taking part in a comedy prank TV show.
One woman is Indonesian and the other is Vietnamese.
Police were already searching for five additional North Koreans, though four are believed to have fled Kuala Lumpur shortly after the attack and are now believed to be back in Pyongyang.
Authorities believe those four provided the poison.
"That's why we asked the North Korean embassy to trace them and hand them over to us," Mr Khalid said.
He said Malaysian authorities had received no help so far from North Korea.
Determining the cause of Mr Kim's death has proven difficult.
Malaysia said on Tuesday that he did not suffer a heart attack and had no puncture wounds such as those a needle would have left, but they were still awaiting lab reports.
Identifying a specific poison can be challenging, especially if a minute amount was used and it did not penetrate fat cells in the victim's tissue.
If the toxin only entered the bloodstream it could leave the body very quickly.
And even if a substance is found, it would need to match the symptoms Mr Kim experienced before his death.
The more unique the poison is, the harder it is to find and highly-sophisticated facilities, such as in Japan or at the FBI's crime lab in the US, are among those that may be needed to discover unusual toxic substances.
The case has perplexed leading forensic toxicologists who study murder by poison.
They say the airport attack is one of the most bizarre cases in the books and question how the two women could walk away unscathed after deploying an agent potent enough to kill Mr Kim before he could even reach hospital.
Mr Khalid noted the two women "were warned to take precautions" and said security camera footage showed them quickly walking to toilets after the attack to wash their hands.
Mr Kim had spent most of the past 15 years living in China and south-east Asia and is believed to have had at least three children with two women.
No family members have come forward to claim the body.
The attack spiralled into diplomatic fury when Malaysia refused to hand over Mr Kim's body to North Korean diplomats after his death, and proceeded with a post-mortem examination over the ambassador's objections.
The two nations have made a series of increasingly angry statements since then, with Malaysia insisting it is simply following its legal protocols, and North Korea accusing Malaysia of working in collusion with its enemy South Korea.
Seoul's spy agency believes North Korea was behind the killing but has produced no evidence.
Isolated North Korea has a long history of ordering killings of people it views as threats to its regime.
Kim Jong Nam was not known to be seeking political power, but was best known for his penchants for drinking, gambling and expensive restaurants.
But his position as eldest son of the family that has ruled North Korea since it was founded could have made him appear to be a danger.
Mr Kim, a heavy-set man in his mid-40s, died soon after the attack en route to a hospital after suffering a seizure, officials say.
He was at the airport to fly to Macau, where he had a home.