Tests will be carried out on an air ambulance station which may have come into contact with victims of the deadly nerve agent Novichok.
Charles Rowley, 45, and Dawn Sturgess, 44, fell ill in Amesbury, near Salisbury, on June 30 after being contaminated by the nerve agent.
Ms Sturgess died eight days after as a result of the poisoning.
Tests are now being carried out on the air ambulance base, emergency vehicles and kit worn by responders who may have come into contact with Charlie or Dawn.
Wiltshire Police said the “highly precautionary process” of tests was designed to ensure that no onward contamination has taken place.
The force said that to allow specialists to carry out their work the ambulance station at Semington will be closed temporarily, and the air ambulance will also be tested and be unable to fly.
Rapid response cars are in place until the air ambulance is back in use.