Forensic investigators will continue to comb for clues in Wiltshire following the latest Novichok poisonings - as police are expected to remain in the county for weeks to come.
Salisbury and nearby Amesbury are being scoured for traces of the potentially deadly nerve agent after Dawn Sturgess, and her partner, Charlie Rowley, were taken ill last Saturday. Both fell ill after "handling a contaminated item" and remain in a critical condition.
Investigators wearing camouflage protective clothing entered the John Baker House assisted-living accommodation in Salisbury, where mother-of-three Ms Sturgess lives, after they took a sample from the outside of the building yesterday.
Other sites visited by the couple in the lead-up to their hospitalisation are also being looked at, as detectives piece together a timeline of the couple's movements. Officers have spoken to several key witnesses, and are trawling through more than 1,300 hours of CCTV which has been collected so far. There was also a heavy operational presence at Mr Rowley's flat, where they were both taken ill.
Police have been unable to locate the source of the contamination and have not ruled out more people falling ill from coming into contact with the substance left over after Sergei and Yulia Skripal were targeted.
The Metropolitan Police said: "Due to the unique challenges involved with this operation, police activity is expected to take weeks and months to complete. The focus of the investigation remains identifying the source of the contamination as quickly as possible."