At least two teams of Russian hitmen were responsible for the Salisbury novichok attack , investigators now believe.
Counter terror police are working on the theory one group arrived on British soil to plant the poison weeks before Sergei Skripal, 67, and his daughter Yulia, 33, were poisoned.
A second team then arrived to administer the nerve agent.
The mission eventually led to the death of Dawn Sturgess, who was poisoned by novichok from a discarded bottle disguised as perfume.
Dawn died after her boyfriend found the poison, believed it was an exotic scent and gave it to her as a present.
Officials believe assassins disguised the poison as perfume to get it through customs and into the UK for the attempt on ex-spy Skripal’s life.
But it was in a sealed box, which raises the terrifying prospect it was NOT the bottle used when novichok was smeared on the Skripals’ front door in March.
If that is the case, the poison used in the assassination bid could have been dumped by killers sent to eliminate the former KGB man in March.
And if it is still out there, somewhere, it could pose a deadly risk to other potential victims.
A Whitehall source said: “The net keeps widening – they almost can’t predict what’s going to turn up next. The bottle they put it in could only have been bought in Russia.
“The suggestion this didn’t come from Russia is almost laughable.
“If this bottle was sealed it means they used another on the Skripals’ front door.
“Where the other one is could be anyone’s guess.”
The source said the killers’ carelessness in concealing the nerve agent inside a Russian product suggests they probably also left the rest of the novichok lying around – regardless of who might find it. One or both groups of hitmen could have been in the UK for a considerable time before the March attack.
Investigators believed the Skripals were watched in the days leading up to the poisoning, when the hitmen identified the best site to administer novichok.
Investigators may have identified two people who could be connected to the attempt on Sergei Skripal’s life through CCTV facial recognition.
But the manhunt could take months, as it is believed the assassins fled Britain after their failed hit.
The Skripals spent weeks in hospital but have been discharged.
While investigators focused intense efforts on tracking the hitmen and the poison, Dawn, 44, fell victim to novichok some three months later.
She died in hospital earlier this month after falling ill when she sprayed it on herself on June 30. Her boyfriend Charlie Rowley, 45, was also exposed to the nerve agent at his home in Amesbury after he found what he thought was a sealed perfume bottle.
Public health officials have now warned people in Wiltshire to steer clear of any unidentified containers. At a public meeting in Salisbury, Mike Wade, from Public Health England, said: “If you did not drop it, do not pick it up.”
Mr Rowley, speaking after he left hospital last week, said he could not remember where he found the bottle of “perfume” which killed Dawn.
He said he often searched through bins for “treasure” and sealed packages often caught his eye.
Officers were seen scouring a local Boots for CCTV footage and have searched various parks around Wiltshire, including Queen Elizabeth Gardens, Salisbury, where it was first suggested Mr Rowley had found the package.
He said Dawn had sprayed the substance on her wrists at his home in Amesbury, eight miles from Salisbury.
He said: “I guess that’s how she applied it and became ill. I guess how I got in contact with it is when I put the spray part to the bottle… I ended up tipping some on my hands, but I washed it off.
“It was an oily substance and I smelled it and it didn’t smell of perfume. It felt oily. I washed it off and I didn’t think anything of it. It all happened so quick.
“Within 15 minutes, Dawn said she had a headache. She asked me if I had any headache tablets. In that time she said she felt peculiar and needed to lie down in the bath. I went into the bathroom and found her in the bath, fully clothed, in a very ill state. It looked expensive, unfortunately it turned out to be a bad find. I think it was very irresponsible for people to leave the poison for anybody to pick up. It could have been children. It was just so unfortunate. I’m very angry at the whole incident.” Meanwhile, Public Health England has helped organise Dawn’s funeral – to make sure mourners are protected.
The Rev Philip Bromiley, who will conduct tomorrow’s crematorium service in Salisbury, revealed “an awful lot of planning” had gone into protecting those attending. He said: “The funeral directors have been liaising with Public Health England and have put various precautions in place. One is that the coffin will be in situ before everybody arrives. I have no concerns.”
The Rev Bromiley said he did not know if Charlie Rowley would be attending. He said: “We will be praying for Charlie at some stage.
“According to the family they do not refer to Charlie as the partner, they just call Charlie a friend.
“Mum and dad are doing really well but they are obviously in a state of shock. They are being positive. Dawn was a really lovely, helpful, giving person.”
He said one of the themes of the service was “praying for peace for the family and for the area as well”.
Dawn’s daughter has chosen the peace hymn Shalom Shalom.