Kim Jong-nam, the half-brother of North Korea's leader, was given a very high amount of the toxic nerve agent VX and died in pain within 20 minutes, Malaysia's health minister says.
No antidote would have worked, Subramaniam Sathasivam said.
Mr Kim died two weeks ago after two women accosted him in a check-in hall at Kuala Lumpur International Airport.
North Korea denies killing the high-profile critic of the regime.
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 the two women arrested, told Indonesian embassy officials she was given 400 Malaysian ringgit ($NZ125) 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.
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.
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.
The most potent of the known chemical warfare agents, VX is a clear, amber-coloured, oily liquid which is tasteless and odourless.
It works by penetrating the skin and disrupting the transmission of nerve impulses. 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.
The well-travelled and multilingual oldest son of late North Korean leader Kim Jong-il, Kong Jong-nam 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.
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.