Novichok, which the Soviets developed in the 1970s and 1980s as a next-generation nerve agent deadlier than others like VX or sarin, was the chemical authorities identified as the substance behind the poisoning of former double agent Sergei Skripal, his daugher Yulia, and a police officer in Salisbury in March.
Sergei Skripal and his daughter survived a nerve gas attack, which Russian Federation denied orchestrating.
He added that Sturgess and Rowley's reactions were so severe that it's believed they came into contact with a high dose of Novichok after handling an infected container which detectives are now seeking.
It was developed in secret by the Soviet Union during the Cold War in the 1980s as a means of countering U.S. chemical weapons defenses, but was revealed to the world by former Soviet scientist and whistleblower Vil Mirzayanov.
Ms Sturgess leaves behind three children.
Police said Sunday they were not yet able to say whether the nerve agent was from the same batch that the Skripals were exposed to.
In addition to Sturgess and Rowley, 21 people have been examined by health experts over concerns they could have been exposed to the Novichok - eight police officers and staff, nine health care workers, one paramedic and three members of the public.
The police's "working hypothesis" is that the Amesbury poisoning and the Salisbury incident are linked, the home secretary said, but he called for the police to be given "time and space" to work. "The government is committed to providing full support to the local community as it deals with this tragedy".
The Ministry of Defence is working with the police on the investigation and the clear-up effort, with 175 armed forces personnel involved.
The Kremlin has said that it was sorry to hear about the death of Ms Sturgess, but said that any suggestion that Russian Federation was involved would be "quite absurd".
"There is no evidence that they visited any of the sites that were decontaminated following the attempted murders of Sergei and Yulia Skripal in March this year", Basu said. "We consider that it is a danger not only for the British, but for other Europeans", Kremlin spokesman Dmitry Peskov told reporters Monday.
George Freeman, a Conservative lawmaker, tweeted that her death "raises quite serious questions" about the assurances from health officials that the risk to the wider public was low.
Professor Paul Cosford of Public Health England has said, however, that "As a precaution we still advise the public not to pick up any odd items such as needles, syringes or unusual containers".
He and Ms Sturgess have been receiving care from the same team at Salisbury District Hospital which successfully treated the Skripals.