Amesbury Novichok police operation 'will take months'
The police operation into the poisoning of a couple with a nerve agent in Salisbury is "expected to take months to complete", officers have said.
Police say Charlie Rowley, 45, and Dawn Sturgess, 44, were exposed to Novichok after handling an unknown object.
The pair remain in a critical condition in hospital a week after falling ill.
Their symptoms were the same as those of Russian ex-spy Sergei Skripal and his daughter Yulia, who were poisoned in March.
No one else has come forward with similar symptoms following the incident, Wiltshire Police said.
Police in hazardous material (hazmat) suits spent Friday searching John Baker House in Salisbury, the hostel where Ms Sturgess lives.
Officers are also looking through more than 1,300 hours of CCTV footage to identify when the couple came in contact with the nerve agent.
Police said the "unique challenges" surrounding the operation meant "police activity is expected to take weeks and months to complete".
Novichok can be degraded by rainwater and sunlight over time - meaning it was probably discovered by the pair in a contained space, a government source said.
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The government blamed the poisoning of the Skripals, both of whom have now left hospital, on the Russian authorities.
Home Secretary Sajid Javid has called on Russia to explain "exactly what has gone on" after another MP, Conservative Tom Tugendhat who chairs the foreign affairs committee, said the latest incident was the result of a "war crime" and "vile act of terror" by Russia.
Russia - which denies involvement in either incident - said the UK was trying to "muddy the waters" and "intimidate its own citizens".
Heatwave impacts search progress
By Frank Gardner, BBC security correspondent
The search for the "source item", the container believed to have poisoned the pair now critically ill in Salisbury hospital, is proving harder than predicted.
Due to the current heatwave, police detectives and chemical weapons experts wearing huge Hazmat (Hazardous Material) suits are only able to spend a few minutes at a time inside the property being searched.
Every single item of possible interest, however small, is having to be assessed as the possible source of the Novichok nerve agent poison and is having to be handled with extreme care.
Whitehall officials are hopeful that the source item will eventually be found - even if it takes months.
Who are the victims?
Ms Sturgess is understood to be a mother of three who lives at the Salisbury hostel, which offers supported accommodation.
A close friend of Ms Sturgess's, who also lived at John Baker House, described her as a "loving and caring person".
Mr Rowley's brother Matthew told the BBC: "He's a lovely guy and would do anything for you. He's a sweetheart basically."
What happened to them?
On Saturday, paramedics were called twice to a flat in Muggleton Road in Amesbury - first at 11:00 BST after Ms Sturgess collapsed.
Medics attended again several hours later, after Mr Rowley also fell ill.
A friend of the couple, Sam Hobson, said after Ms Sturgess was taken to hospital, he and Mr Rowley went to a chemist in Amesbury to collect a prescription before going to an event at a nearby Baptist church.
The two men returned to the flat and planned to visit the hospital but Mr Rowley "started feeling really hot and sweaty" and began "acting all funny", Mr Hobson, 29, said.
"He was rocking against the wall and his eyes were red, pinpricked, and he started sweating loads and dribbling, so I had to phone an ambulance for him," said Mr Hobson.
Based on information from a friend and items found at the flat, Wiltshire Police initially thought the pair had fallen ill after using a contaminated batch of heroin or crack cocaine.
But after tests at the government's military research facility at Porton Down, a major incident was declared and it was confirmed they had been exposed to Novichok.
What are the police investigating?
Police do not believe Mr Rowley and Ms Sturgess were victims of a targeted attack, but instead came into contact with the substance in Amesbury or Salisbury.
On Friday night, police revealed more details around the victim's movements.
They said the pair were both at John Baker House at lunchtime on 29 June, before visiting a number of shops in Salisbury and heading to Queen Elizabeth Gardens.
They returned to the hostel at about 16:20 BST before heading to Amesbury by bus at about 22:30.
Police believe they were there until emergency services were called on Saturday.
Five areas have been cordoned off: Muggleton Road, Boots pharmacy and the Baptist church in Amesbury; John Baker House and Queen Elizabeth Gardens in Salisbury.
Public Health England has repeated its "highly precautionary advice" for people who had visited those five locations but stressed there was no immediate health risk.
PHE advised washing worn clothes with a regular detergent at normal temperature, wiping items like phones and handbags, and double-bagging dry-clean only items, with further instructions to follow on those.
Mr Javid said the "strong working assumption" was that the pair came into contact with Novichok in a location which had not been cleaned up following the Skripal poisoning.
Assistant Commissioner of Specialist Operations Neil Basu said that "around 100 detectives" from the Counter Terrorism Policing Network were working on the investigation.
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