A couple found unconscious in Wiltshire county in South West England on Saturday were exposed to the nerve agent Novichok, the same gas that poisoned Russian ex-spy Sergei Skripal and his daughter in March, police officials said on Thursday.

The couple, believed to be Charlie Rowley and Dawn Sturgess, fell ill at a house in Amesbury town of Wiltshire on Saturday, the BBC reported. They are now in hospital in critical condition. Amesbury is about eight miles (12.87 kms) from Salisbury, the place where Skripal was poisoned.

The defence research facility at Porton Down science park conducted tests on the substance that poisoned the couple, and found it to be Novichok. The science park is located near Wiltshire county. Chemical weapons expert Richard Guthrie told BBC that the couple may have come across the nerve agent in a syringe or pot, as it could have been disposed off “in a haphazard way”.

The police said no other individuals have shown the same symptoms as Rowley and Sturgess. They added that there was “nothing in their background” to suggest that the couple was targeted.

Metropolitan Police Assistant Commissioner Neil Basu said it was not yet clear whether the nerve agent came from the same batch that Skripal and his daughter Yulia were exposed to, but said the police were exploring that possibility. No contaminated items have been found, but the police are analysing the couple’s movements, he added.

“We have no idea what may have contained the nerve agent at this time,” he said. Basu added that the Counter Terrorism Policing Network was now leading the inquiry.