British counter-terrorism police said on Friday they believed they had found the source of the Novichok nerve agent that killed a woman in southwest England and left her partner critically ill in hospital.
A bottle found at Charlie Rowley's Amesbury house was tested by scientists at Porton Down, the Met Police said.
Dawn Sturgess, 44, from Durrington, died in hospital on Sunday evening after being exposed to the nerve agent the previous weekend.
You can receive Breaking News on a smartphone or tablet via the BBC News App. Police have interviewed Rowley in recent days since he recovered consciousness.
"However, we can not guarantee that there isn't any more of the substance left", said Assistant Commissioner Neil Basu, Head of UK Counter Terrorism Policing.
The incident occured just miles from where ex-spy Sergei Skripal, and daughter Yulia, were attacked with the substance in Salisbury in March.
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"We want to make it clear that there is no cordon in place and once the vehicle has been removed, police will leave the scene and it will be open to the public as normal".
"This is clearly a significant and positive development".
An investigation is now under way to establish whether it is from the same batch that poisoned Sergei and Yulia Skripal in Salisbury in March. "However, we can not guarantee that there isn't any more of the substance left and cordons will remain in place for some considerable time", Metropolitan Police Assistant Commissioner Neil Basu said in a statement.
"This is to allow thorough searches to continue as a precautionary measure for public safety and to assist the investigation team".
The British government previously blamed the attempted assassination of Sergei Skripal on Russian Federation, which Russia denies.
The case led the United States and other countries to expel a large number of Russian diplomats.