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.
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.
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.
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