North Korea used a weapon of mass destruction, VX nerve agent, to murder one man in Malaysia last month, settling an old family feud.

But that is not the only time the regime in Pyongyang has been linked to the use of deadly chemicals. In Syria in 2013 the Assad regime, reportedly with the assistance of the North Korean military, used the chemical weapon sarin and possibly VX as well to kill people in far greater numbers. More than 1,400 people died, of whom more than 400 were children. And if there is another war on the Korean Peninsula, hundreds of thousands will be killed by chemical agents in the Kim family’s arsenal.

Pyongyang claims it does not possess such weapons. The North, however, has not signed the Chemical Weapons Convention, so there is no verification.

“Of those handful of states that have not acceded to the convention, the most threatening, by far and away, is North Korea,” veteran Pentagon advisor Robert Collins tells The Daily Beast.

In fact, North Korea wants us to know how dangerous it is, and it sent a powerful message by using fast-acting VX in an airport terminal in Kuala Lumpur to kill Kim Jong Nam, the elder half-brother of Supreme Leader Kim Jong Un.

The assassination of this Kim family member is almost certainly not the North’s only murder using a chemical. Choi Duk-kun, a South Korean diplomat, died in Vladivostok in 1996. His body showed a puncture wound and traces of neostigmine bromide, which attacks the nervous system. Seoul, with justification, blames North Korea for the killing. Pyongyang issued a denial.

There are also well-founded suspicions the North murdered Christian activist Patrick Kim, who died in the Chinese border city of Dandong in 2011 with spots on his fingers, foam in his mouth, and neostigmine bromide in his body.

The killings of diplomat Choi and activist Kim were conducted out of sight of the international community. Not so the assassination of Kim Jong Nam. The public nature of the act highlights both the boldness of ruler Kim Jong Un and the nature of the Kim family system.

As Sung-Yoon Lee of Tufts University’s Fletcher School told me last week, “The latest terrorist act using a deadly banned chemical substance in a very public place in a foreign country with thousands of innocent bystanders from the world over passing by shows that the Kim regime is as vile as any in modern history.”

That vile regime has one of the world’s largest arsenals of chemical weapons, holding, according to a 2014 estimate by South Korea’s Defense Ministry, between 2,500 and 5,000 tons of deadly compounds.

Pyongyang’s production facilities look like they operate around the clock. “The biggest weakness of chemical weapons is that their effectiveness expires soon and new supplies need to be made constantly, so North Korea maintaining a stockpile of up to 5,000 tons indicates a very strong production capability,” notes Kim Dae Young of the Korea Defense and Security Forum in South Korea. Analysts think the North can produce 4,500 tons of chemical agents a year but is able to surge to 12,000 tons a year.

The North maintains a minimum of eight locations manufacturing about 25 varieties of deadly compounds including sarin, mustard, tabun, and hydrogen cyanide in addition to nerve agents like VX.

The stockpile, Collins says, “is enough to kill every South Korean several times over.” Analysts Victor Cha and David Kang believe the Korean People’s Army can fire 500,000 artillery rounds on Seoul in the first hour of the next war. Many of those shells would contain chemical agents.

The opening hours, therefore, would devastate the South Korean capital, only 35 miles from the Demilitarized Zone separating the two Koreas. At a minimum, there would be tens of thousands of casualties in that city during the first day. The conflict would be, as Clinton-era official Kurt Campbell told ABC News, “a horrific symphony of death.”

We got a glimpse of such a symphony in Syria. President Bashar al-Assad used chemical weapons on his own people beginning, it appears, in late 2012, and he could not have done so without the Kim regime’s extensive technical assistance, which began in the mid-1990s. There were several reported interceptions of various North Korean shipments of chemical weapons gear en route to Syria.

Bruce Bechtol of Angelo State University wrote in 2013 that North Korea had designed and built in Syria at least two chemical weapons facilities. Moreover, he pointed out that the North helped build chemical warheads, specifically supplying components and providing expertise.

North Korean officers were spotted at a number of Syrian locations, including chemical weapons facilities. Three North Koreans reportedly were killed in 2007 at a Syrian military base in Aleppo during the loading of mustard gas on a Scud missile. A major in the Syrian army, who had defected after serving in a chemical weapons branch, said the North’s military personnel were providing training in their use.

Apparently there was also “after-sales service.” North Koreans served on the front lines of the civil war, reportedly helping the Syrians use chemical weapons on the battlefield, most notably in 2013 around the embattled city of Aleppo, near the site of a chemical weapons attack.

As Bechtol, author of North Korea and Regional Security in the Kim Jong Un Era, points out, Pyongyang was the Assad regime’s primary supplier of chemical weapons and their delivery systems.

The North apparently lost a customer when Syria acceded to the Chemical Weapons Convention in October 2013 and the U.S. and Russia brokered a deal to destroy Assad’s chemical munitions, but Pyongyang has been merchandising deadly chemicals elsewhere. Leading analyst Joseph Bermudez, among others, believes North Korea has sold Iran these weapons.

We care about Pyongyang’s chemical weapons not only because of murders in Malaysia, China, and Russia and wholesale slaughter in Syria, but also because, as Bermudez notes, the North has “the ability to employ these weapons worldwide using unconventional methods of delivery.”

In this regard, Lee Yun Keol of the North Korea Strategic Information Service Center in Seoul believes Kim’s technicians are probably thinking of putting chemical compounds on the tips of long-range missiles. The North already is believed to have three missiles with sufficient range to hit the lower 48 states.