LONDON (AP) — British forensic investigators are continuing to search for the source of the lethal nerve agent that poisoned two people who are hospitalized in critical condition.

Officials think 44-year-old Dawn Sturgess and 45-year-old Charley Rowley were exposed to the same chemical weapon used in the March attack on a Russian ex-spy and his daughter.

Sergei and Yulia Skripal were poisoned in southwest England not far from where Sturgess and Rowley live.

Police have said they are looking for a vial that may contain Novichok, a nerve agent made in the Soviet Union during the Cold War.

Officials have said the search underway Saturday could take weeks or months. It has brought more than 100 officers to Salisbury and Amesbury as suspect sites are condoned off to protect the public.