Kim Jong Nam's Mysterious Death: What Poison May Have Killed Him?

Update (23 February 8:20 p.m. ET) | Malaysian police have reported that VX nerve gas was used to kill Kim Jong Nam, following a preliminary analysis of material collected from facial swabs of the victim.

More than a week after the murder of Kim Jong Nam, the 45-year-old half-brother of North Korean leader Kim Jong Un, observers are still wondering exactly how he was killed. According to news reports, Kim died shortly after two women apparently rubbed or sprayed substances on his face in the Kuala Lumpur airport on February 13. The bizarre murder has ratcheted up tensions between Malaysia and North Korea and led to an international investigation into who is behind the killing; South Korea accused its northern neighbor of the deed, though they've denied involvement.

Many believe Kim was poisoned. But with what? And why the need for two alleged assassins? Likewise, if the two suspects did in fact have poison on their hands, how are they still alive? Malaysia hasn't released results of an autopsy, but several toxicology and poison experts have a few theories about what might have happened.

John Trestrail, a forensic toxicologist and author of a book about homicidal poisonings, said it is theoretically possible to create a "binary poison" from two chemicals that would be harmless in separation, but deadly when combined (which would explain why neither woman was injured). However, he doesn't think this is exceedingly likely. "I've studied well over 1,000 cases [of murder with poison] and I can't think of any" that employed such an approach, he says.

There are several types of poisons that can be deadly in minute quantities when absorbed through the skin or inhaled, though Trestrail declined to name any specific examples. "I'm not willing to identify that information—I don't want to put that in anybody's hands," he says. He also is not aware of any fatal poisonings using a chemical absorbed through the skin, though he is familiar with a few unsuccessful attempts to do so.

There are several nerve agents that can kill in small amounts, via absorption and inhalation, such as sarin, soman and VX, says Paul Wax, a physician and executive director of the American College of Medical Toxicology. Of course, if these were used in the Kim killing, the poisoner would've had to be careful not to get it on their own skin, and might have had to wear gloves, he says. These chemicals generally work by interfering with the transmission of nerve signals, and often kill by stopping breathing and/or violently shutting down the nervous system.

However, other experts question this possibility, since nerve agents may be difficult to contain and often cause extreme irritation and blistering, and this apparently wasn't the case according to photographs, says Bruce Goldberger, medical toxicologist at the University of Florida College of Medicine.

Cyanide is another possible culprit. This age-old poison is deadly in small quantities, and certain formulations can be absorbed through the skin. Plus, cyanide may be turned into a deadly gas when mixed with an acid, says Greene Shepherd, a doctor of pharmacy and professor at the University of North Carolina.

Goldberger, the University of Florida toxicologist, says the alleged attackers could've used carfentanil, an extremely potent synthetic opioid that's 10,000 times stronger than morphine and can kill in tiny quantities. If the women had taken an antidote called naloxone, they may have been prevented from being harmed if exposed through their skin. (There's some evidence that the Russian military used an aerosolized form of carfentanil to subdue armed Chechens who took hostages at a Moscow theater in 2002.)

Natural substances like tetrodotoxin and saxitoxin, produced respectively by pufferfish and algae, are another possibility, says University of Arizona toxicologist Mazda Shirazi. These are potent neurotoxins and can be absorbed through the skin or inhaled.

Of course, until the autopsy results are released, and more information is known about exactly what happened to Kim in the aftermath of the attack, it's impossible to know what killed him. As Trestrail, the forensic toxicologist, puts it: we need to "look at the victim—that's where the secret is."