Theories Abound in New Nerve-Agent Poisoning in U.K.

LONDON — As the British government scrambled to explain a second nerve-agent poisoning of two people in southwestern England, experts on Thursday were weighing a range of theories about how this could happen again.

Police said Wednesday that a British couple had been sickened in Amesbury, England, by Novichok, the nerve agent developed in the Soviet Union and used to poison Sergei V. Skripal, a former Russian spy, and his daughter, Yulia Skripal, on March 4 just a few miles away, in Salisbury.

The government blamed Russia for the initial attack, an accusation the Kremlin denied, and the case heightened diplomatic tensions, leading Britain and its Western allies to expel scores of diplomats, and prompting Russia to retaliate.

The poisoning of Charlie Rowley, 45, and his girlfriend, Dawn Sturgess, 44, in Amesbury could be an accidental consequence of the attack on the Skripals, or it could be a separate assault, experts say, though it was unclear why the recent victims would have been targeted.

Rowley and Sturgess were being treated at the same hospital that had cared for the Skripals, who survived the attack after spending weeks in a coma.

Analysts and other experts put forward multiple theories about how the recent poisoning could have occurred.

The nerve agent could have been left on, or in, a discarded object by whoever poisoned the Skripals. It could have been accidentally spread by someone else who had come into contact with it. Or the person who planted it on Sergei Skripal’s front door may have intentionally left it at another location, just to muddy the waters.

“I would put it in the 90 percent-plus likelihood that this was in a discarded item” like a coat with a container of the nerve agent in a pocket, said Richard Guthrie, coordinating editor of CBW Events, a website on chemical and biological weapons.

Andrew C. Weber, a former U.S. assistant secretary of defense for nuclear, chemical and biological defense programs, said, “It is quite possible that the couple touched a container, applicator or protective gear that was used in the original Russian Novichok attack.”

That hypothesis is plausible, but so are others, said Dan Kaszeta, a former chemical and biological weapons adviser to the White House and the U.S. Secret Service. “There’s too many variables here,” he said.

Russia categorically denies involvement in either case, said Dmitry Peskov, a spokesman for President Vladimir Putin. “We are, of course, concerned after all by the repeated use of such substances in Europe,” he said in a conference call with reporters. “Although, on the other hand, we do not have information about what kinds of substances were used, how they were used.”

Russian officials quickly offered alternative theories, as they did after the Skripal poisoning, including one that says the British could have planted the nerve agent. Sergei Zheleznyak, a deputy speaker of the Russian Parliament, suggested that British authorities had concocted the case to sully Russia’s image while the country hosts the World Cup.

“A huge number of British fans, despite the warnings from their government, came to support their team,” Zheleznyak told state television. “Their impressions are just destroying everything British propaganda built over the past few years. To break up this flow of really positive emotions that the British fans are sharing, they had to put something like this in the mass media.”

Nikolai Kovalyov, a former director of the Federal Security Service, the successor to the KGB, suggested a rogue scientist from the Porton Down laboratory, near Salisbury, was conducting experiments on people living nearby.

The Russian Embassy in the Netherlands wrote on Twitter, “How dumb they think” Russia is to stage the latest attack while Russia is hosting the soccer tournament, a publicity boon.

On Thursday, Sajid Javid, the British home secretary, said that the nerve agent that poisoned the couple in Amesbury was the same one used to target the Skripals, but he did not say whether it was from the same batch of Novichok.

“We can anticipate further disinformation from the Kremlin, as we saw following the Salisbury attack,” he told the House of Commons. “Many of you will question whether this incident is linked to that one. That is clearly the main line of inquiry. However, we must not jump to conclusions.”

On social media, critics of the British government questioned how the nerve agent could have survived for four months without breaking down into less-harmful components.

But experts had an explanation: “The stuff is relatively persistent — it’s designed to last a long time,” Kaszeta said.

That would be especially true if the toxin were suspended in a gel, eh said, adding that it was a strong theory among investigators looking into the March attack. A thinner liquid would be more easily broken down if it came into contact with water, but a gel would repel water. Police have made it clear in the Skripal case that “this stuff is very persistent in the environment,” Guthrie said.

In addition, he said, a container — a syringe wrapped in a plastic bag or a screw-top plastic jar — would have protected the agent from water and decay.

As for how much of the substance the Skripals’ assailant had, “that’s anybody’s guess,” Kaszeta said, and could depend on how clean or sloppy the operation was.

“Were the guys who did this given more than they needed?” he asked. “The container might even have fingerprints on it. It’s a smoking gun, but killers sometimes even leave a smoking gun at the scene of a crime.”