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The banned chemical weapon VX nerve agent was used to kill Kim Jong Nam, the North Korean ruler's outcast half brother who was attacked by two women who rubbed the substance on his face at the airport in Malaysia's capital last week, police said Friday.

Authorities were checking the Kuala Lumpur airport for traces of the toxin, 11 days after the attack. But news that a powerful nerve agent was used to kill someone in a crowded airport raised serious questions about public safety.

Police said one of the alleged attackers had been vomiting after the Feb. 13 attack, but there were no reports that anyone else had been sickened.

VX nerve agent, deadly even in minute amounts, was detected on Kim's eyes and face, Malaysia's inspector general of police said in a written statement, citing a preliminary analysis from the country's Chemistry Department.

"Our preliminary finding of the chemical that caused the death of Kim Chol was VX nerve," said Inspector-General of Police Khalid Abu Bakar. Kim Chol is the name on the passport found on the victim, but a Malaysian official previously confirmed he is North Korea leader Kim Jong Un's older half brother.

Malaysian police had previously said no one besides Kim Jong Nam had been sickened. But Khalid told reporters that one of the two women accused of wiping the toxin on Kim's face became sick later and suffered from vomiting. He declined to say which woman had been sick, the Indonesian woman or the Vietnamese woman in custody.

Khalid said police were still investigating how the lethal agent entered Malaysia.

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Police previously said the airport had not been decontaminated but that passengers should be confident it was safe. Asked Friday in a text message whether it had still not been decontaminated, Khalid said, "We are doing it now."

Details were not immediately clear.

VX nerve agent has the consistency of motor oil and can take days or even weeks to evaporate. It could have contaminated anywhere Kim was afterward, including medical facilities and the ambulance he was transported in, experts say.

The death of Kim Jong Nam, whose daylight assassination in a crowded airport terminal seems straight out of a spy novel, has unleashed a diplomatic crisis, especially as speculation grows that Pyongyang dispatched a hit squad to Malaysia to kill the exiled older sibling of North Korean leader Kim Jong Un.

North Korea has denounced Malaysia's investigation as full of "holes and contradictions" and manipulated by Pyongyang's enemies.

According to Malaysian investigators, the two female suspects coated their hands with the liquid toxin and wiped it on Kim's face on Feb. 13 as he waited for a flight home to Macau, where he lived with his family.

He sought help from airport staff but he fell into convulsions and died on the way to the hospital within two hours of the attack, police said.

Malaysian police say the women washed their hands immediately as they'd been trained to do while handling the substance.

Dr. Bruce Goldberger, a leading toxicologist who heads the forensic medicine division at the University of Florida, said even a tiny amount of VX nerve agent — equal to a few grains of salt — is capable of killing. It can be administered through the skin, and there is an antidote that can be administered by injection. U.S. medics and military personnel carried kits with them on the battlefield during the Iraq war in case they were exposed to the chemical weapon.

"It's a very toxic nerve agent. Very, very toxic," he said. "I'm intrigued that these two alleged assassins suffered no ill effect from exposure to VX. It is possible that both of these women were given the antidote."

He said symptoms from VX would generally occur within seconds or minutes and could last for hours starting with confusion, possible drowsiness, headache, nausea, vomiting, runny nose and watery eyes. Prior to death, a victim would likely have convulsions, seizures, loss of consciousness and paralysis.

VX is banned under the Chemical Weapons Convention, which North Korea never signed. The country is believed by outside experts to have the capacity to produce up to 4,500 metric tons of chemical weapons during a typical year, which it could increase to 12,000 tons per year during a period of crisis. Its current inventory has been estimated at 2,500 to 5,000 tons.

It is suspected of being particularly focused on mustard, phosgene, sarin and V-type chemical agents — substances including VX that are designed to poison through contact and remain lethal for long periods of time. The North's development of such agents has been of special concern because of fears it might try to put them in artillery shells for an attack on South Korea's capital, potentially threatening the lives of millions.

Joseph Bermudez, a well-known North Korea analyst, wrote an article for the respected 38 North website in 2013 that said the North is capable of not only employing "significant quantities and varieties of chemical weapons" across the Korean Peninsula but also using those weapons worldwide "using unconventional methods of delivery."

He also said there is a "growing body of evidence" indicating the North has shared chemical weapons capabilities with Syria, Iran and others.

In addition to the suspected attackers, Malaysia has arrested a North Korean man said to be an information technology worker at a Malaysian herbal supplements company and is seeking at least seven people, including the second secretary of North Korea's embassy in Kuala Lumpur.

While Malaysia isn't one of Pyongyang's key diplomatic partners, it is one of the few places in the world where North Koreans can travel without a visa. As a result, for years, it's been a quiet destination for Northerners looking for jobs, schools and business deals.