VX nerve agent, a chemical on a UN list of weapons of mass destruction, was used to kill the estranged half-brother of North Korean leader Kim Jong Un in last week's bizarre murder in a busy Kuala Lumpur airport, Malaysian police said on Friday.
Kim Jong Nam died on February 13 after being assaulted by two women who wiped the toxic chemical on his face as he prepared to board a flight to Macau at Kuala Lumpur International Airport.
Malaysian police were investigating whether the illegal VX - believed to be the most toxic known nerve agent - was brought into the country of made there, and authorities were sweeping the airport and other locations for radioactive material.
"If the amount of the chemical brought in was small, it would be difficult for us to detect," Khalid Abu Bakar told reporters.
Police arrested the two women - one Vietnamese and the other Indonesian - and a North Korean man last week. They are also seeking seven other North Koreans wanted in connection with the case, including a diplomat at the embassy in Kuala Lumpur.
South Korean and US officials have said they believe North Korean agents assassinated Kim Jong Nam, who had been living in the Chinese territory of Macau under Beijing's protection.
North Korea is believed to have the world's third-largest stockpile of chemical weapons, according to the Nuclear Threat Initiative project, which analyses weapons of mass destruction.
South Korean analysts have identified sarin and VX as the focus of the North Korean chemical weapons program.
Police said swabs taken from the eye and the face of the North Korean murder victim revealed the presence of VX nerve agent, or S-2 Diisoprophylaminoethyl methylphosphonothiolate.
"Other exhibits are under analysis," Khalid said in a statement that cited findings from a preliminary report from the government's chemical weapons analysis unit.
Khalid said the two women who were paid to carry out the assault had washed their hands before fleeing from the airport.
But he said one of them was suffering from the effects of the chemical and was vomiting.
Airport camera footage released on Monday by Japanese broadcaster Fuji TV shows the moment they assaulted Kim Jong Nam. In later clips he is seen asking airport officials for medical help, and rubbing his eyes and stumbling as he entered an airport clinic. He died on the way to hospital.
MOST TOXIC NERVE AGENT
VX is tasteless and odourless, and is outlawed under the Chemical Weapons Convention, except for "research, medical or pharmaceutical purposes". It can be manufactured as a liquid, cream or aerosol. Experts said VX has no commercial uses.
"This is not something you make in a kitchen lab. This is something that is made in a very sophisticated chemicals weapons lab," said Bruce Bennet, a senior defense researcher at the California-based RAND Corporation.
VX in liquid form can be absorbed into the body through skin or eye contact and does not evaporate easily so it can persist in the environment. After giddiness and nausea, exposure to VX quickly progresses to convulsions and respiratory failure before death, according to the US Centers for Disease Control and Prevention (CDC).
Absorbed in large doses, it is fatal after 15 minutes, according to the US Army's Edgewood Chemical Biological Center, making it the world's most toxic known nerve agent.
In 2015, traces of sarin and VX nerve agent were found at a military research site in Syria that had not been declared to the global chemical weapons watchdog.
SUSPECTS WANTED
Malaysian authorities on Thursday requested Interpol to put an alert out to apprehend four North Korean suspects who are believed to have fled Malaysia on the day of the attack.
They also want to question the second secretary at the North Korean embassy, though he has diplomatic immunity, and are seeking two other North Koreans, including an employee at the state-owned airline Air Koryo, who are still believed to be in Malaysia.
The investigation has resulted in fraught relations between two countries that had hitherto maintained friendly ties.
North Korea has said the Southeast Asian nation should be held responsible for the killing of one of its citizens, though it has not acknowledged that the victim is the half brother of the North Korean leader Kim Jong Un.
Malaysia has recalled its ambassador from Pyongyang for consultations.
