The finding, by a German military laboratory, set off alarm bells across Western capitals 13 months ago: A powerful Soviet-era nerve agent was found in the tissue of Russian anti-corruption crusader Aleksei Navalny, lying comatose in a Berlin hospital.
Laboratories in France and Sweden followed suit. And the finding was then reconfirmed by the Nobel Prize-winning organization that employs some of the world's best scientists and is charged with regulating, monitoring, and stopping the use of chemicals weapons worldwide.
Two dozen years ago, the world's most sweeping treaty aimed at eliminating chemical weapons came into effect. In addition to establishing The Hague-based Organization for the Prohibition of Chemical Weapons (OPCW), the treaty set up a way for its 193 members to raise suspicions and accusations -- and a way to investigate or verify them using inspectors.
That may be about to happen for the first time in the OPCW's history.
A group of 45 countries is pushing Russia to provide a full explanation of the circumstances behind Navalny's illness, which occurred in August 2020 as he was traveling in Siberia. He was evacuated to Berlin, where doctors saved his life and later identified the poison that nearly killed him.
The toxin came from the Novichok family, a group of deadly substances that were developed by the Soviet Union in the 1980s as part of that country's vast, secret, sprawling chemical- and biological-weapons program. Along with the United States, the Soviet Union, and later Russia, developed the world's largest arsenals of chemical weapons.
Russia has pushed back, in a 235-page document that took direct aim at the initial October 5 letter from the 45 OPCW members, as well as attacking some of Navalny's colleagues.
One of the most important tools available under the 1997 Chemical Weapons Convention is something called a Challenge Inspection. Essentially, this allows for a country to demand that a team of OPCW inspectors be dispatched to another country to verify whether that country is producing chemical weapons.
It has never been done before.
"If Russia is making small quantities of these agents, and they're using them against people, it's a violation of the convention," Marc-Michael Blum, an expert formerly with the OPCW, told RFE/RL. He added that whether "a Challenge Inspection can reveal that, however, [is] an open question."
Britain, meanwhile, is among the 45 countries leading the charge. That's due to the fact that in March 2018, some two years before Navalny's poisoning, Novichok was identified in the near-fatal poisoning in England of former Russian intelligence officer Sergei Skripal and his daughter, Yulia. A British woman named Dawn Sturgess later died after being accidentally exposed to a container that had Novichok in it.
The discovery stunned experts and arms-control advocates who had accepted, and hailed, Russia's announcement the previous year that it had destroyed its entire chemical-weapons arsenal.
London blamed the Skripal poisoning on Russian intelligence agents.
Navalny and his associates have also blamed Russian intelligence, an assertion bolstered by open-source researchers at Bellingcat, who identified the intelligence officers and scientific institutes they alleged were involved in the effort.
In March 2021, after an unexplained delay, and then again in August, the United States imposed sanctions on several of the Russian institutes in question, and Russia's main domestic security agency, the Federal Security Service.
"The poisoning of [Navalny] on Russian soil was a clear instance of a situation causing doubt about compliance with the Convention, and specifically of Russia's observance of its obligations under the Convention," the British representative to the OPCW wrote on October 18.
"The clear message of the 45" countries that have joined the British effort, Blum said, was "'we will not let this rest.'"
Russia's Foreign Ministry did not immediately respond to two e-mails sent by RFE/RL seeking further comment.
In its response to the first letter, however, Russia cast aspersions on the German-led investigation, asserting that it was "aggressively pushing a far-fetched version" that Navalny was targeted with a Novichok-related toxin.
"The Russian side has repeatedly and in great detail set out its vision of what is happening around A. Navalny, giving fact-based assessments of the whole situation and presenting a chronology of events for public review," the Russian representative office said in its letter dated October 7.
Western countries have said they don't believe Russia has been transparent or forthcoming with its information or answers.
Few international experts expect Russia to conduct a transparent criminal investigation into the use of a chemical weapon against one of its own citizens. The question, experts say, is then whether a Challenge Inspection by the OPCW is the only tool available.
"Russian obfuscating and telling outright lies, that's nothing new," said one U.S. official with direct knowledge of the international discussions to pressure Moscow under the treaty. "The question is, how do you address that under the treaty structure?"
"Skripal, Navalny: They are attempted assassinations. The treaty wasn't designed for those sorts of circumstances," said the official, who was not authorized to speak publicly and spoke on condition of anonymity.
The 41-member Executive Council of the OPCW is not scheduled to meet until sometime early next year. The larger grouping, called the Conference of State Parties, will be meeting later in November, though few expect any tangible progress to come out of that.
Under treaty rules, meanwhile, a country could force the issue by demanding a special, unscheduled meeting of the Executive Council. It's unclear whether Britain, or any of its allies, is preparing to push that option. Treaty rules also allow a country to demand a Challenge Inspection without going through the Executive Council.
The problem is that the treaty was set up to address the mass-scale production of chemical weapons, for which a country would have large factories or storage facilities to produce and stockpile the materials. With inspections, those are easy to investigate and hard to conceal.
If Russia indeed has a formal system of producing Novichok or other toxins or nerve agents, however, it is likely to be small-scale, experts say: easy to conceal, and easy to hide any traces or evidence of production.
That provides a disincentive for a country to demand a Challenge Inspection; the country must have ironclad certainty that an inspection team will find something. Otherwise, it will severely undermine the credibility of the accusing party, and possibly the OPCW inspectors.
"I don't think there will be a request for a Challenge Inspection," said Gregory Koblentz, director of the Biodefense Graduate Program at George Mason University outside of Washington, D.C. "The Russians have had plenty of time to sanitize sites involved in Novichok production.
"Unless the Brits have exquisite intelligence on where to sample to find traces of Novichoks or degradation compounds, then a [Challenge Inspection] is a high-risk endeavor," he said in an e-mail. "If the Brits actually do have intel that good on the Novichok program, would using it to target the [Challenge Inspection] risk blowing their source or method?"
The U.S. official said Western intelligence agencies had had suspicions about Russia's declarations dating back at least to 2002, when Chechen terrorists took hundreds of people hostage at a Moscow theater. The crisis ended when security forces pumped a secret gas derived from fentanyl into the building, rendering the hostages and their captors unconscious. About 130 hostages died.
"You don't just have large quantities of a fentanyl-based toxin lying around unless you have a production and storage system in place. That was a clear indication" Russia may be continuing such programs, the U.S. official told RFE/RL.
"We've been concerned about a program for a long time," the official said. "We've been surprised, disappointed, to find out now that these chemicals are being used in these sorts of assassination programs."