A British woman died after being poisoned with a nerve agent. The UK blames Russia.

Just four months ago, an ex-Russian spy was exposed to the same poison in Britain.

A woman has died in the United Kingdom after being poisoned by a military-grade nerve agent — and Russia may be to blame.

Dawn Sturgess and Charles Rowley, British citizens in their mid-40s, fell ill in their home in Wiltshire, England last week. The two were taken to the hospital on June 30 and were in critical condition. Sturgess, a mother of three, died Sunday evening, prompting a murder investigation. Rowley remains in critical condition in the Salisbury District Hospital.

Police initially thought a contaminated batch of illegal drugs was to blame, but UK Home Secretary Sajid Javid said on Thursday that authorities now believe the couple was exposed to Novichok, the same lethal poison that was used in the attempted assassination of former Russian spy Sergei Skripal and his adult daughter last March.

The UK police haven’t yet determined whether the two cases are linked. “They are unable to say at this moment whether or not the nerve agent found in this incident is linked to the attack on Sergei and Yulia Skripal,” Neil Basu, assistant commissioner for counterterrorism with London’s Metropolitan Police, told reporters on Monday.

But it’s probably a safe bet: The Skripal attack took place just eight miles from where Sturgess and Rowley live, in the town of Amesbury in the southern region of England. That incident prompted a massive decontamination effort that took several months to complete and cost about £7.5 million, which is about $9.9 million in USD.

Javid, the home secretary, said last week that the couple likely came into contact with Novichok at another site that wasn’t part of the clean-up operation. Experts say that the toxin degrades so slowly that it’s possible the couple came into contact with it well after the original attack.

British police believe the couple was exposed to a contaminated item, but have yet to locate it.

“Their reaction was so severe, it resulted in Dawn’s death and Charlie being critically ill. This means that they must have got a high dose and our hypothesis is that they must have handled a container we are now seeking,” Basu said.

British citizens are now on high alert, uncertain whether the deadly poison is still lurking in other places. Although England’s Chief Medical Officer Sally Davies told the public there’s a low risk of contamination, she advised people to wash their clothes and wipe down their personal belongings.

Why Russia was likely behind the poisonings

British authorities blamed Russia for the Skripal poisoning back in March and expelled 23 Russian diplomats in retaliation — the UK’s largest removal of foreign officials in more than 30 years. In a joint statement on March 15, the leaders of the US, UK, France, and Germany said it was “highly likely that Russia was responsible for the attack.”

Yet Russian President Vladimir Putin continues to deny allegations that the Kremlin was involved. Following Sturgess’ death, Kremlin spokesman Dmitry Peskov said Russia was “deeply concerned” about the poisoning, but called the allegations “absurd.”

But Moscow makes sense as a potential culprit. After all, the Soviet Union created Novichok throughout the 1970s and 1980s, and the Russian government has continued to produce it.

The Kremlin also had a motive: Sergei Skripal was a member of a Russian intelligence service, known as the GRU, who was convicted in 2006 of handing over the names of 300 Russian agents to the British. Skripal admitted to helping UK spies for at least a decade.

The couple that was poisoned on Saturday, on the other hand, so far don’t seem to have connections to Russia. It seems they were just accidental victims.

Britain has already pointed the finger at Russia.

“The Russian state could put this wrong right. They could tell us what happened, what they did and fill in some of the significant gaps that we are trying to pursue,” Britain’s security minister, Ben Wallace, told BBC radio on Thursday.

The Skripals survived, and continue to recover from the attack — but it’s unclear if Rowley will be as lucky.

Meanwhile, London clearly wants to keep the pressure on the Kremlin. “The eyes of the world are currently on Russia, not least because of the World Cup,” Javid told Parliament on Thursday. “It is now time that the Russian state comes forward and explains what has gone on.”