Searches are expected to continue for several weeks, if not months, as officers look for other possible sites or sources of contamination, as well as gather further evidence.
Dawn Sturgess, 44, died a week ago after she apparently handled a bottle contaminated with the nerve agent in Amesbury, Wiltshire.
Her partner Charlie Rowley, 45, remains in hospital where he is in a serious but stable condition.
Their exposure comes after ex-Russian spy Sergei Skripal and his daughter Yulia were poisoned with the same substance in Salisbury in March.
They recovered after many weeks in hospital.
Meanwhile, Ms Sturgess’s friends are planning their own memorial for her on Friday afternoon which is “open to anyone and everyone”.
Ryan Knight, who knew Ms Sturgess through their time at the Salisbury homeless shelter John Baker House, said: “A lot of us probably won’t be allowed to go to the funeral.
“I don’t want to disgrace her funeral.
“I prefer not to turn up rather than get dirty looks.
“I’ll be in the background.
“When her immediate family go, I’ll go over and pay my respects.”
Mr Knight described Ms Sturgess, who had three children, as having had ” lots of friends”, adding that the manner of her death was “something which is never expected”.
“These are two innocent people.”
Meanwhile, scientists at the Defence, Science and Technology Laboratory at Porton Down are carrying out further tests to confirm whether Ms Sturgess and her partner were affected by the same batch that poisoned the Skripals.
It is not yet clear where the contaminated bottle came from and how it came to be in Mr Rowley’s home, where it was found.
Assistant Commissioner Neil Basu, head of UK Counter Terrorism Policing, said: “We cannot guarantee that there isn’t any more of the substance left, and cordons will remain in place for some considerable time.
“This is to allow thorough searches to continue as a precautionary measure for public safety and to assist the investigation team.”
Ms Sturgess’s post mortem examination is scheduled to take place on Tuesday and an inquest into her death is set to open and adjourn in Salisbury on Thursday.