Since the Russian government originally had the only samples of this, British authorities, including Prime Minister Theresa May, have concluded that there can only be two options: either Russia is behind the attacks or they let their custom-made nerve agent fall into the hands of someone else.
Paramedics were called on Saturday morning to a house in Amesbury, a few miles from Salisbury, after the woman, named by media as Dawn Sturgess, collapsed.
-10.30 p.m. They catch a bus to Amesbury.
-12.20 p.m. The man and woman are together at John Baker House in Salisbury.
Police confirmed the pair had been left critically ill in a hospital.
-1.45 p.m. He visits the Amesbury Baptist Centre on Butterfield Drive. Charlie Rowley is also present at the address.
Drones are being used to scan the park.
A swab was taken from the outside of the Rollestone Street building, which is now heavily cordoned and lined by forensic tents.
Incident response vehicles and fire engines joined police at his Amesbury home.
Police have been unable to locate the source of the contamination and have warned that they can not rule out more people falling ill.
The hostel is a short walk away from Zizzi's - the restaurant where Skripal and his daughter had their last meal before falling ill.
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He believes they must "have gone somewhere contaminated" in Salisbury.
One theory understood to be under investigation is that the pair poisoned in the latest incident may have inadvertently found a container - such as a phial or syringe - used to transport the nerve agent for the initial attack on the Skripals and discarded in a public place.
Ben Jordan, a friend, described Mr. Rowley as a scavenger who would pick up cigarette butts from the ground and often go through the trash cans outside charity shops in search of something he could use or sell.
This is Neil Basu of the British Metropolitan Police.
"The focus of the investigation remains identifying the source of the contamination as quickly as possible".
"As before, my advice is to wash your clothes and wipe down any personal items, shoes, and bags, with cleansing or baby wipes before disposing of them in the usual way", she said.
"I know that many of you will question whether this incident is linked to that one", Javid said, referring to the Skripal poisoning.
Two people in Amesbury, England, have been poisoned by the same nerve agent that almost killed a former Russian spy and his daughter earlier this year.
The Russian Embassy accused the United Kingdom of trying to "frighten its own citizens".
While agents of the Novichok class were highly lethal, the program was only partly successful, as some of the components were as toxic as the military-grade nerve agents and thus hard to handle safely.