Kim Jong-nam, the half-brother of North Korea's leader, was given a very high amount of the toxic nerve agent VX and he died in pain within 15-20 minutes, Malaysia's health minister says.
No antidote would have worked, said Subramaniam Sathasivam.
Mr Kim died two weeks ago after two women accosted him in a check-in hall at Kuala Lumpur International Airport.
They say they thought they were doing a TV prank. North Korea denies killing the high-profile critic of the regime.
Who could be behind the attack?
Unravelling the mystery of Kim Jong-nam's death
VX is classified as a weapon of mass destruction by the United Nations. A drop on the skin can kill in minutes.
Indonesian national Siti Aisyah, 25, one of two women held, told Indonesian embassy officials that she was given 400 Malaysian ringgit ($80; £72) to smear Kim Jong-nam's face with "baby oil" as part of a reality show joke.
Doan Thi Huong, a Vietnamese national born in 1988, has also said she thought she was taking part in a television prank.Image copyright Reuters Image caption Tens of thousands of passengers have gone through the airport since the murder took place
Malaysian police say the attackers had been trained to wash their hands immediately after the attack.
Some experts have suggested that they might have each smeared two different non-lethal elements of VX, which became deadly when mixed on Mr Kim's face.Image copyright EPA Image caption Siti Aisyah "met some people who looked Japanese or Korean", Indonesian officials said
A North Korean man has also been arrested in connection with the killing.
At least seven other suspects are wanted for questioning by police, including Hyon Kwang Song, 44, second secretary at the North Korean embassy in Kuala Lumpur.
On Sunday, Malaysian authorities swept the airport and declared it safe.
They are also analysing samples found at a flat said to have been rented by suspects.
What is the deadly VX nerve agent?Image copyright Science Photo Library Image caption Molecular model of VX nerve agent shows atoms represented as spheres
- The most potent of the known chemical warfare agents, it is a clear, amber-coloured, oily liquid which is tasteless and odourless
- Works by penetrating the skin and disrupting the transmission of nerve impulses - a drop on the skin can kill in minutes. Lower doses can cause eye pain, blurred vision, drowsiness and vomiting
- It can be disseminated in a spray or vapour when used as a chemical weapon, or used to contaminate water, food, and agricultural products
- VX can be absorbed into the body by inhalation, ingestion, skin contact, or eye contact
- Clothing can carry VX for about 30 minutes after contact with the vapour, which can expose other people
- Banned by the 1993 Chemical Weapons Convention
Read more about VXMedia captionRupert Wingfield-Hayes: Three reasons why the use of VX is so extraordinary
Who was Kim Jong-nam?
The well-travelled and multilingual oldest son of late North Korean leader Kim Jong-il, he was once considered a potential future leader. He has lived abroad for years and was bypassed in favour of his half-brother, Kim Jong-un.Image copyright AP Image caption North Korea has not identified the man who died as Kim Jong-nam, only as a North Korean citizen
He had been travelling on a passport under the name Kim Chol. North Korea has yet to confirm that the deceased was actually Kim Jong-nam.
For many years, it was believed Kim Jong-nam was being groomed to succeed his father as the next leader.
But that appears to have come to an end in 2001 when Kim was caught sneaking into Japan on a fake passport.
He later became one of the regime's most high-profile critics, openly questioning the authoritarian policies and dynastic succession his grandfather Kim Il-sung began crafting in 1948.
Kim Jong-nam, North Korea's critic in exile