Around 200 military personnel are believed to be still helping with the clean up in the city following the attack. (Image: MoD/Crown Copyright).
Police are believed to have identified the suspected perpetrators of the Salisbury nerve agent attack.
A source inside the Police told the Press Association:
"Investigators believe they have identified the suspected perpetrators of the Novichok attack through CCTV and have cross-checked this with records of people who entered the country around that time.
"They (the investigators) are sure they (the suspects) are Russian."
Officers think several Russians were involved in the attempted murder of the former double agent Sergei Skripal and his daughter Yulia using the nerve agent, Novichok.
They are believed to still be looking for more than one suspect.
The news comes as an inquest is due to open into the death of Dawn Sturgess, 44, who died eight days after also being exposed to the nerve agent in Amesbury.
Her partner Charlie Rowley, 45, was left fighting for his life after also being contaminated by the chemical.
Police believed they had come into contact with a Novichok-contaminated item.
Investigators are working to the theory that the substance was in a discarded perfume bottle found by the couple in a park or somewhere in Salisbury city centre which Ms Sturgess sprayed Novichok straight on to her skin, the source said.
It is understood Ms Sturgess was exposed to at least 10 times the amount of nerve agent the Skripals came into contact with.
The Metropolitan Police declined to comment.
On Wednesday, a fingertip search of Queen Elizabeth Gardens in Salisbury was carried out as military personnel continue to help with decontamination work around the city.
The park and other locations in Salisbury and nearby Amesbury were all cordoned off last month.
Last week counter-terrorism detectives revealed they had found a small bottle containing Novichok at Mr Rowley's home in Muggleton Road, Amesbury.
They are trying to establish where the container came from, and how it came to be in his house.
International experts from the Organisation for the Prohibition of Chemical Weapons (OPCW) was called in to independently verify the substance and they have since finished collecting samples.
Public Health England said the risk to the public remains low but it continued to "strongly advise" not to pick up any unknown "strange items" such as syringes, needles, cosmetics or similar objects made of materials such as metal, plastic or glass.