British Prime Minister Theresa May said Monday that it was “highly likely” that Russia was responsible for poisoning former Russian spy Sergei Skripal and his daughter in Salisbury, England, last week. “It is now clear that Mr. Skripal and his daughter were poisoned with a military-grade nerve agent of a type developed by Russia,” the prime minister explained. The Russian ambassador to London has been summoned to explain the incident, which may have put hundreds of people at risk of contamination. May said that either the attack was a “direct act” of the Russian government or that the Russians had lost control of one of their nerve agents. (The Russian government denied any involvement.) If it’s the former, the attack raises the question of whether this incident constitutes a chemical weapons attack by Russia on British soil.
Skripal and his daughter Yulia are still in critical condition after they were found slumped on a park bench on March 4. The officer who found them is also still in the hospital but is communicative. At least 21 people received medical attention, and hundreds more who visited the restaurant where the nerve agent has been detected may have been exposed and have been urged to wash their clothes.
These casualty numbers are not far off from those of some recent chlorine gas attacks in Syria that have reportedly prompted the White House to consider military action against Bashar al-Assad’s regime—which would presumably be justified as an enforcement of the Chemical Weapons Convention. Secretary of Defense James Mattis has even said, in regard to Syria, that nerve agents are of particular concern when it comes to punishing the use of chemical weapons.
The Skripal poisoning wasn’t a battlefield attack, of course, but the Chemical Weapons Convention, of which both Russia and Britain are signatories, prohibits the use of toxic chemicals such as nerve agents except for a few, specifically described purposes; assassinating ex-spies on foreign soil is not one of them.
Matthew Meselson, a molecular biologist who co-directs the Harvard-Sussex Program on Chemical and Biological Weapons, told me by email that “if a nerve agent is deliberately used or even retained by a state” for a purpose not specified under the convention, that would be a violation. On the other hand, “if the use of a nerve agent is not actually ordered by a state, regardless of the nationality of the perpetrators, that use would not be in violation of the CWC. As you can imagine, proving that a state actually ordered such use, even defining what a state is in such a case, could present difficulties.”
Just last week, the U.S. slapped new sanctions on North Korea over the use of the nerve agent VX in the assassination of leader Kim Jong-un’s estranged half-brother in Malaysia last year. State Department spokeswoman Heather Nauert described that attack as a “public display of contempt for universal norms against chemical weapons use [that] further demonstrates the reckless nature of North Korea and underscores that we cannot afford to tolerate a North Korean WMD program of any kind.”
The open—and very difficult to answer—question of whether Moscow ordered the hit or merely lost possession of the nerve agent leaves London a bit of wiggle room in how it responds, but not much. The British government was widely criticized for its tepid response to the 2006 poisoning of former FSB agent Alexander Litvinenko with radioactive polonium. While a government inquiry concluded that President Vladimir Putin “probably” approved the killing, former Prime Minister David Cameron was reluctant to respond harshly, in an effort to avoid exacerbating tensions with Russia. The fact that May even pointed the finger at Moscow this soon is a sign that things have changed, and evidence of just how egregious this attack was.