Police believe they have identified the suspected perpetrators of the Novichok nerve agent attack on Sergei Skripal and his daughter Yulia.
Officers think several Russians were involved in the attempted murder of the former Kremlin double agent in Salisbury back in March.
It is understood that the suspected assassins have been recorded on CCTV, which has then been cross-checked with records of people entering the UK at that time.
It comes as an inquest opens today into the death of Dawn Sturgess, 44, who died this month after apparently coming into contact with the same batch of Novichok.
It is believed that she found a bottle of the nerve agent after it had been disposed of by the attackers three months before.
Scroll down for video
Police believe they have identified the suspected perpetrators of the attack on Russian former spy Sergei Skripal and his daughter Yulia (pictured in Salisbury before the were hospitalised)
It comes as an inquest opens today into the death of Dawn Sturgess (pictured), who died this month after apparently coming into contact with the same batch of Novichok
Wednesday saw officers begin a painstaking search of Queen Elizabeth Gardens in Salisbury, Wiltshire, where they believe the couple came across the Novichok in a perfume bottle
Her partner Charlie Rowley, 45, was left fighting for his life after also being contaminated by the chemical weapon.
It is understood mother-of-three Ms Sturgess was exposed to at least 10 times the amount of nerve agent the Skripals came into contact with.
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.
Mr Rowley says that after finding the bottle, Ms Sturgess sprayed Novichok straight on to her both of her wrists, the source said.
The Metropolitan Police, who are leading the investigation, declined to comment.
But a source with knowledge of the investigation 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.’
According to reports from US security officials, police have recovered grainy CCTV images of persons who inadvertently killed Dawn.
Dawn Sturgess (left), 44, died last week, and her partner Charlie Rowley (right), 45, is fighting for life in hospital after they found the Russian nerve agent in Amesbury, near Salisbury
Police outside Mr Rowley’s home in Amesbury, Wiltshire, on July 5 after he and Ms Sturgess picked up a perfume bottle containing the chemical weapon Novichok
A police officer stands guard over a cordoned off rubbish bin after Dawn Sturgess and Charlie Rowley fell ill in Amesbury
Counter-terror cops are closing in on identifying the suspects, thought to be from Mr Skripal’s former employers, Russia’s military intelligence service the GRU.
Both he and his daughter, as well as Detective Sergeant Nick Bailey, of Wiltshire Police, made miraculous recoveries after being on the brink of death.
All three were treated at Salisbury General Hospital, where Charlie is now being cared for.
The perfume bottle could support the theory that a woman was involved in the initial hit by up to six people against Sergei and Yulia Skripal in Salisbury on March 4.
Ms Sturgess’ inquest will be opened today in Salisbury and the hearing is expected to be adjourned to allow police inquiries to continue.
On Wednesday, a fingertip search of Queen Elizabeth Gardens in Salisbury was carried out.
Moscow strenuously denies poisoning Yulia (pictured) and her ex-spy father Sergei Skripal four months ago
Forensic police officers wearing hazmat suits prepare to examine a vehicle believed to belong to Sergei Skripal on March 8
Police stand guard outside the Salisbury home of Sergei Skripal, who nearly lost his life despite only coming into contact with a small amount of nerve agent, police believe
The park and other locations in Salisbury and nearby Amesbury were cordoned off last month after the exposure of the couple to the nerve agent.
Searches of properties could last months after 400 items were recovered, officers warned, while waste and litter will be removed as part of the sweep of public areas.
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.
A team of international experts from the Organisation for the Prohibition of Chemical Weapons (OPCW) was called in to independently verify this.
They have finished collecting samples which will now be analysed at two OPCW labs before the results are reported back to the UK.
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.