Fire and Rescue Service personel arrive with safety equipment at the site of a housing estate on Muggleton Road, after it was confirmed that two people had been poisoned with the nerve-agent Novichok, in Amesbury, Britain, July 6, 2018.
Police say the nerve agent that sickened Rowley and Sturgess was the same type that nearly killed the Skripals, but scientists haven't been able to tell whether it was from the same batch.
Police suspect Rowley and Sturgess handled a discarded item from the first attack, though they have not determined for certain that the two cases are linked.
Russia, now hosting the soccer World Cup, has denied any involvement in the March incident and suggested the British security services carried out the attack to stoke anti-Moscow hysteria.
"Police and security officials are working urgently to establish the facts of this incident, which is now being treated as murder", May said.
"The Government is committed to providing full support to the local community as it deals with this tragedy", she wrote in a second tweet.
He said: "Ms Sturgess was an innocent member of the public who should have been able to go about her daily life without becoming an unwilling victim in such an unprecedented, international, incident".
Counterterrorism police are also studying roughly 1,300 hours of closed circuit television footage in hopes of finding clues about the couple's activities in the hours before they became violently ill.
Prime Minister Theresa May said police were still hard at work investigating the source of the nerve agent.
She said: "The staff here at Salisbury District Hospital worked tirelessly to save Dawn".
Skripal and his daughter were both released from the hospital this spring. Still, more than 20 other countries have expelled Russian diplomats in a show of support for the UK.