Dawn Sturgess, 44, died from her exposure to the nerve agent on Sunday, while Charlie Rowley, 45 is in critical condition at the Salisbury District Hospital. Five hours after her collapse, police said, an ambulance was called back to the same address for Rowley, who also fell ill and was taken to the hospital.
British police rushed to solve a murder mystery on Monday after a woman died following exposure to the nerve agent Novichok, four months after the same toxin almost killed a former Russian spy in an attack that Britain blamed on Moscow.
One line of inquiry suggests that after the Skripals were attacked by the nerve agent, the assailants disposed of vials, ampules or a mixing kit - or some other contaminated items - and that Rowley and Sturgess found the material and were accidentally exposed.
Basu said that Sturgess leaves behind three children, and offered thoughts and prayers for the woman's family.
The three other men have been tested and show no signs of having been exposed to novichok.
Sturgess and a man named locally as Charlie Rowley, 45, fell ill last weekend in Amesbury, near the town of Salisbury where former double agent Sergei Skripal and his daughter Yulia were attacked with Novichok in March and have since recovered.
On March 12, British Prime Minister Theresa May says the military-grade nerve agent has been identified as belonging to the Novichok ("Newcomer") group, which was developed by the Soviet government towards the end of the Cold War.
The company said: 'When we posted the design of the Novichok on Behance (social network for designers), we got a huge number of negative reactions.
Mr Deputy Speaker, this of course is a very upsetting time - not just for Dawn's family, but also for the people of Amesbury and Salisbury who have seen places they know and love cordoned off and become a murder investigation scene.
Assistant Commissioner Neil Basu, the head of UK Counter Terrorism policing, said Sturgess' death was "shocking and tragic news".
Police are continuing to hunt for a contaminated container which they believe was handled by the pair.
Britain blames the Russian state for the attack on Sergei Skripal and 33-year-old Yulia - an allegation Moscow has repeatedly denied.
Her death comes four months after the poisoning of.
"We continue to be deeply anxious by the continuing presence of these poisonous substances on British territory", Peskov told reporters.
Britain blames Russian Federation for the attack on the Skripals, an allegation Moscow has repeatedly denied.
After the Skripal attack, Britain tossed out two dozen Russian diplomats suspected of being intelligence agents.
The force added: "The current advice from Public Health England is that the risk to the public remains low". The unknown item remains at the centre of police investigations, which are likely to continue for several weeks.
Britain "understands that direct dialogue between the two superpowers is capable of reducing the level of confrontation, gradually raising the level of trust between our countries, and destroying the lies fabricated against Russia", Zheleznyak said in July 9 comments released by his party.