In 1994 and 1995, the Japanese cult Aum Shinrikyo used homemade VX to attack three people, one of whom died. 
 
 North Korea is estimated to have a chemical weapons production capability of up to 4,500 metric tons during a typical year and 12,000 tons during a period of extended crisis. It is widely reported to possess a large arsenal of chemical weapons, including mustard, phosgene and sarin gas, a United States Congressional Research Service report said last year. 
 
 The announcement by Malaysia’s police chief came just a day after North Korea denied any responsibility for Mr. Kim’s death, accusing the Malaysian authorities of fabricating evidence of Pyongyang’s involvement under the influence of South Korea. 
 
 With the North’s reclusive government on the defensive about the Feb. 13 killing of Mr. Kim, the estranged half brother of Kim Jong-un, at the airport for the Malaysian capital, Kuala Lumpur, a statement attributed to the North Korean Jurists Committee said the greatest share of responsibility for the death “rests with the government of Malaysia” because Kim Jong-nam died there. And in what could be seen as a threat to Malaysia, the statement noted that North Korea is a “nuclear weapons state.” 
 
 But in a case that has been filled with mysteries and odd plot twists, North Korea still would not acknowledge that the man killed was indeed Kim Jong-nam. And it gave no indication that it would agree to Malaysia’s demands to question a senior staff member at the North Korean Embassy in Kuala Lumpur in the investigation into Mr. Kim’s death. 
 
 Relatives and acquaintances of the two women Malaysia has accused of carrying out the killing, by applying poison to Kim-Jong-nam’s face as North Korean agents looked on, insisted they must have been duped into doing so, though the Malaysian authorities say otherwise. 
 
 “I don’t believe Huong did such a thing,” said Doan Van Thanh, father of Doan Thi Huong, 28, a Vietnamese woman being held in Malaysia. “She was a very timid girl. When she saw a rat or frog, she would scream.” ||||| Media playback is unsupported on your device Media caption Rupert Wingfield-Hayes: Three reasons why the use of VX is so extraordinary 
 
 Kim Jong-nam, the half-brother of North Korea's leader, was killed by a highly toxic nerve agent, says Malaysia. 
 
 Mr Kim died last week after two women accosted him briefly in a check-in hall at a Kuala Lumpur airport. 
 
 Malaysian toxicology reports indicate he was attacked using VX nerve agent, which is classified as a weapon of mass destruction by the United Nations. 
 
 There is widespread suspicion that North Korea was responsible for the attack, which it fiercely denies. 
 
 It responded furiously to Malaysia's insistence on conducting a post-mortem examination and has accused Malaysia of having "sinister" purposes. 
 
 What does the toxicology report say? 
 
 Malaysia's police chief Khalid Abu Bakar said on Friday that the presence of the nerve agent had been detected in swabs taken from Mr Kim's eyes and face. 
 
 One of the women Mr Kim interacted with at the airport on 13 February had also fallen ill with vomiting afterwards, he added. 
 
 Mr Khalid said other exhibits were still under analysis and that police were investigating how the banned substance might have entered Malaysia. 
 
 "If the amount of the chemical brought in was small, it would be difficult for us to detect," he said. 
 
 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 VX 
 
 Who could be behind the attack? 
 
 How could it have killed Mr Kim? 
 
 Media playback is unsupported on your device Media caption CCTV footage appears to show the moment Kim Jong-nam is attacked 
 
 Bruce Bennett, a weapons expert at the research institute the Rand Corporation, told the BBC it would have taken only a tiny amount of the substance to kill Mr Kim. 
 
 He suggests a small quantity of VX - just a drop - was likely to have been put on cloths used by the attackers to touch his face. A separate spray may have been used as a diversion. 
 
 Mr Khalid has previously said the fact the woman who accosted Mr Kim immediately went to wash her hands showed she was "very aware" that she had been handling a toxin. 
 
 It would have begun affecting his nervous system immediately, causing first shaking and then death within minutes. 
 
 More from expert Bruce Bennett 
 
 Is Kuala Lumpur airport safe? 
 
 The authorities say they intend to decontaminate the airport and areas the suspects are known to have visited. 
 
 VX is a v-type nerve agent, which means the substance can remain lethal for a long period of time. 
 
 "It's as persistent as motor oil. It's going to stay there for a long time... which means anyone coming in contact with this could be intoxicated from it," forensic toxicologist John Trestrail told the Associated Press news agency. 
 
 No passengers, airport workers or medical staff who treated Mr Kim were reported to have become ill in the aftermath of the incident, the news agency adds. 
 
 Tens of thousands of passengers are believed to have passed through the airport since the attack more than 10 days ago. 
 
 Who was Kim Jong-nam? 
 
 Image copyright AP Image caption North Korea has not identified the man who died as Kim Jong-nam, only as a North Korean citizen 
 
 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. 
 
 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 Stalinist policies and dynastic succession his grandfather Kim Il-sung began crafting in 1948. 
 
 Kim Jong-nam: North Korea's critic in exile 
 
 How did he die? 
 
 A woman was seen in CCTV footage approaching Mr Kim and wiping something across his face. He sought medical help at the airport, saying someone had splashed or sprayed him with liquid. 
 
 He had a seizure and died on the way to hospital. 
 
 His body remains in the hospital's mortuary, amid a diplomatic dispute over who should claim it. 
 
 Main players in mysterious killing 
 
 Who did it? 
 
 Malaysia says it was clearly an attack by North Korean agents. Four people are in custody, including one North Korean and the two women he interacted with at the airport. Seven North Koreans are being sought, including a diplomat. 
 
 There are a number of North Korean organisations capable of directing such an attack, including the exclusive Guard Command. 
 
 The North hit back at Malaysia on Thursday, saying it was responsible for the death of one of its citizens. 
 
 In response, Malaysian Foreign Minister Anifah Aman warned North Korean envoy Kang Chol on Friday that he would be expelled unless he stopped "spewing lies" about the attack. 
 
 Who in North Korea could organise a VX murder? 
 
 North Korea's history of foreign assassinations 
 
 Does North Korea have VX? 
 
 North Korea is one of just six countries not to have signed the Chemical Weapons Convention (CWC) arms control treaty banning the production, stockpiling and use of chemical weapons. 
 
 According to the Nuclear Threat Initiative project, however, North Korea is thought to have the third largest stockpile of chemical weapons, after the US and Russia. 
 
 South Korea's defence ministry estimated in 2014 that the North has somewhere between 2,500 and 5,000 tonnes of nerve agents in stock, with VX identified as among them. ||||| FILE - In this May 4, 2001, file photo, a man believed to be Kim Jong Nam, the eldest son of then North Korean leader Kim Jong Il, looks at a battery of photographers as he exits a police van to board... (Associated Press) 
 
 FILE - In this May 4, 2001, file photo, a man believed to be Kim Jong Nam, the eldest son of then North Korean leader Kim Jong Il, looks at a battery of photographers as he exits a police van to board a plane to Beijing at Narita international airport in Narita, northeast of Tokyo. Police in Malaysia... (Associated Press) 
 
 KUALA LUMPUR, Malaysia (AP) — The banned chemical weapon VX nerve agent was used to kill Kim Jong Nam, the North Korean ruler's outcast half brother who was poisoned last week at the airport in Kuala Lumpur, police said Friday. The announcement raised serious questions about public safety in a building that authorities went 11 days without decontaminating. 
 
 The substance, 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. 
 
 Khalid told reporters that one of the two women accused of wiping the toxin on Kim's face was later sickened and suffered from vomiting. He declined to say which of the women — one Indonesian and one Vietnamese — had gotten sick. 
 
 Khalid said police were still investigating how the lethal agent entered Malaysia. 
 
 Police previously said the airport had not been decontaminated. Asked Friday in a text message whether that was still the case, Khalid said, "We are doing it now." Details were not immediately clear. 
 
 Malaysian police also previously no one besides Kim Jong Nam had been sickened. 
 
 If VX was used, it could have contaminated not only the airport but anyplace else Kim had been, including medical facilities and the ambulance he was transported in. The nerve agent, which has the consistency of motor oil, can take days or even weeks to evaporate. 
 
 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 that escalates by the day. With each new twist in the case, international speculation has grown 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 accused the authorities here of being in cahoots with Pyongyang's enemies. 
 
 According to Malaysian investigators, the two female suspects coated their hands with chemicals and wiped them 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. 
 
 The case has perplexed toxicologists, who question how the two women could have walked away unscathed after handling a powerful poison, even if — as Malaysian police say — the women were instructed to wash their hands right after the attack. 
 
 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, there would likely be 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. 
 
 Malaysia has three people in custody in connection with Kim Jong Nam's death, including the two suspected attackers. Authorities are also seeking several other people, including the second secretary of North Korea's embassy in Kuala Lumpur and an employee of North Korea's state-owned airline, Air Koryo. 
 
 The case has marked a serious turnaround in relations between Malaysia and North Korea. 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. 
 
 ___ 
 
 AP writers Margie Mason in Jakarta, Indonesia, and Eric Talmadge in Tokyo contributed to this report.
– Kim Jong Nam's assassins killed him with a banned chemical weapon, Malaysian police revealed Friday. The country's police chief said toxicology reports on swabs from the face and eyes of the exiled North Korean found VX nerve agent, which the BBC notes is classed as a weapon of mass destruction by the United Nations. He said that one of two women believed to have rubbed the extremely toxic substance on Kim's face with their hands suffered from vomiting after the attack. The New York Times reports that VX agent can be created by mixing two compounds—and police suspect the two women put the substances on Kim's face, one after the other, to create a deadly dose. The police chief said the airport where Kim was attacked is now being decontaminated. North Korea—which is widely suspected to have been behind the killing of leader Kim Jong Un's half brother—never signed the Chemical Weapons Convention that banned VX, the AP notes. Pyongyang denies involvement and says Malaysia's investigation is full of "holes and contradictions." The father of one of the two women being held, Vietnamese citizen Doan Thi Huong, tells the Times his daughter trained as a pharmacist and he has seen little of her in recent years. (Police say that after Malaysia refused to give Kim's body to North Korean diplomats, somebody tried to break into the morgue.)