In the 12 months since the shocking attack, some 250 detectives have worked on the investigation, collecting more than 11,000 hours of CCTV footage and 1,700 statements from the public.
The site has been declared decontaminated after an almost year-long military clean-up operation.
The decontamination is part of a scheduled programme to make Salisbury and Amesbury safer.
The helicopter was grounded while tests were carried out.
Officers are expected to be wearing protective clothing,
Dawn Sturgess is believed to have been exposed to nerve agent from gift Rowley picked up.
His mother’s body is currently 'property of the Crown'.
It has also been revealed that the nerve agent ‘could remain active for 50 years’