Dawn Sturgess died after being exposed to the nerve agent Novichok. On Monday, police said they had transported a van from Swindon, around 30 miles (48 km) from Amesbury, in connection with the investigation.
Metropolitan Police Assistant Commissioner Neil Basu said it was implausible that the attack on the Skripals in Salisbury in March, and the poisonings nearby of Ms Sturgess and Mr Rowley were not linked.
Basu, who is national lead for Counter Terrorism Policing, told residents of Amesbury he would "love to be able to say that we have identified and caught the people responsible and how we are certain there are no traces of nerve agent left anywhere in Wiltshire, but the brutal reality is that I can not offer you any reassurance or guarantee at this time". Moscow rejected the accusations and hit back by expelling Western diplomats. We sincerely apologise if any offence was caused, especially to the families of Dawn Sturgess and Charlie Rowley, and understand the timing of the release of this product may have lacked sensitivity.
Officials say the substance was manufactured in the then-Soviet Union during the 1970s and can be picked up by merely handling a contaminated item. He said he could not guarantee there are no further traces of the lethal poison in the area.
The Skripals fell ill after the poison was applied to the ex-spy's front door in the city of Salisbury.
Basu said he hopes Rowley continues to improve and can give police details about the location of the container.
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The official added that China has warned the USA that future actions would be met with "economic attacks" on American markets. Proposed tariffs on another US$200 billion of Chinese imports have been rolled out with Beijing vowing to retaliate.
"At this stage, we can not say with certainty that both the incident in March and this latest incident are linked, " Basu told attendees at Tuesday evening's community meeting. "Our focus and priority at this time is to identify and locate any container that we believe may be the source of the contamination". Medical workers initially suspected a drug overdose but tests by the Porton Down military research centre showed they had been exposed to Novichok.
The UK government has blamed Russian Federation for the incident, but the authorities in the Motherland deny any involvement.
Britain has notified the global chemical weapons watchdog, the Organisation for the Prohibition of Chemical Weapons (OPCW). Sergei and Yulia Skripal became seriously ill, but have both recovered.
Sturgess died at Salisbury District Hospital, the same facility that nursed the critically ill Skripals. Her father was discharged on May 18.
A police officer stands at a cordon around a public litter bin next to a supported housing project in Salisbury on July 5 after two people were exposed to Novichok nerve agent.