Horrific images from the aftermath of a suspected chemical weapons attack in Syria are once again circulating online. The scene of this gassing is the eastern Ghouta suburb of Damascus. Both the location and the timing of this apparent war crime are symbolically important. And while the immediate focus will be on Syrian dictator Bashar al-Assad and his willingness to gas his own people, any long-term solution will require understanding the role of the rogue states that enable and support him.

It was one year ago, on the morning of April 7, 2017, that the Trump administration launched punitive airstrikes against Assad's regime at the Shayrat Airfield in response to a Sarin gas attack days earlier. Those targeted bombings were intended to send a message to Assad: Stop using banned weapons of war against your own people. Assad was undeterred.

He had failed to adhere to a previous deal, negotiated by the Obama administration and Russia, that was intended to end his chemical weapons capability. The concord was struck in the aftermath of the August 21, 2013, nerve agent attack on eastern Ghouta–the same suburb hit in the last 24 hours. The U.S. government determined that the Assad regime was responsible and "that 1,429 people were killed … including at least 426 children."

Just a few weeks later, in September 2013, the U.S. and Russia agreed to "special procedures" for the "expeditious destruction of the Syrian chemical weapons program and stringent verification thereof." Secretary of State John Kerry claimed in 2014 that the agreement had worked, saying "we got 100 percent of the chemical weapons out" of Syria. That obviously wasn't true, or at least highly misleading, as Assad retained the capability to regenerate and use certain weapons.

And now—one year after the U.S. attempted to punish Assad with airstrikes, and in the same neighborhood that was terrorized in 2013— the Syrian regime has seemingly struck again.

Many details concerning this most recent attack remain to be confirmed. But the world has already learned some valuable lessons regarding the behavior of rogue actors when it comes their pursuit and use of banned weapons.

There is no real question that Assad has continued to use chemical weapons even after he agreed to give them up. As the State Department was quick to note yesterday, the U.S. has concluded that he was responsible for the April 4, 2017, Sarin gas attack in Khan Sheikhoun—the same incident which prompted the Trump administration's bombing. And both the U.S. government and the UN have found that Assad's goons used other chemical weapons, namely crude chlorine bombs, more than once. While some of these bombs struck areas held by jihadi rebels, they have also indiscriminately killed civilians.

Assad's principal international backer, Vladimir Putin, hasn't stopped him from using of them. Nor has Iran, which is deeply embedded in Syria alongside Assad's forces. In fact, the Assad-Putin-Khamenei axis has a legion of online apologists who argue that the high-profile chemical weapons assaults aren't really the work of the Syrian "president" at all. This noxious advocacy on behalf of mass murderers is readily available on social media.

It gets even worse, as another rogue state has reportedly facilitated Assad's acquisition of chemical weapons: North Korea. This facilitation is especially worrisome in light of the two nations' previous cooperation on a nuclear reactor that was destroyed by the Israelis in 2007.

In March, the U.N. issued a report on North Korea's active "prohibited military cooperation projects…stretching from Africa to the Asia-Pacific region, including ongoing ballistic missile cooperation with the Syrian Arab Republic and Myanmar, widespread conventional arms deals and cyberoperations to steal military secrets."

The U.N. traced a number of visits by North Korean officials to Syrian soil, finding that "multiple groups of ballistic missile technicians" have been inside Syria. Citing intelligence received from a "Member State," the U.N. explained that these "technicians … continued to operate at chemical weapons and missile facilities at Barzah, Adra and Hama." The Assad regime tried to deflect this accusation by claiming the North Koreans were in town simply for "training athletics and gymnastics."

But the U.N. documented additional suspicious details, including previously unknown illicit shipments and transfers. The U.N. investigative body's "investigations into several cases of hitherto unreported arms shipments and cooperation with front companies of designated entities between 2010 and 2017 showed further evidence of arms embargo and other violations, including through the transfer of items with utility in ballistic missile and chemical weapons" programs.

In one such transfer, the North Koreans provided the Assad regime with "special resistance valves and thermometers known for use in chemical weapons" programs. U.N. member states also interdicted suspicious shipments, including bricks and tiles that may be used as part of a chemical weapons program. Although the U.N. found these specific materials weren't banned, a member state noted that they "can be used to build bricks for the interior walls of [a] chemical factory."

The U.N. found it especially suspicious that North Korean front companies were doing business with the Syrian government's Scientific Studies and Research Center (SSRC), which oversees Assad's chemical weapons development.

The U.S. Treasury Department sanctioned 271 SSRC staffers in the aftermath of the April 2017 Sarin gas attack in Khan Sheikhoun. Treasury explained that the SSRC is "the Syrian government agency responsible for developing and producing non-conventional weapons and the means to deliver them." And the sanctioned SSRC employees "have expertise in chemistry and related disciplines and/or have worked in support of SSRC's chemical weapons program since at least 2012."

Therefore, the U.N.'s conclusion that North Korea has been working with the SSRC is especially noteworthy.

The U.S. and its allies will continue to face daunting challenges when it comes to restraining rogue nations and their pursuit of banned weapons. As Syria's ongoing work on chemical weapons shows, such proliferation concerns often involve multiple rogue states. Assad's chemical weapons attacks inside Syria are principally his own doing, but not solely. He has friends outside of Syria who are willing to help.