There is no evidence to suggest they went to any areas that had been decontaminated after the attack on Sergei Skripal and his daughter Yulia, who were exposed to the nerve agent in Salisbury in March.
He said scientists would continue to establish if the nerve agents are from the same batch, but that the Defence, Science and Technology Laboratory at Porton Down are "already crystal clear" that both are Novichok.
The 45-year old is in critical but stable condition.
Police seized a vehicle in Swindon on Monday as part of their ongoing investigation into the poisoning.
Staff at Salisbury District Hospital said Mr Rowley has made a "a small but significant improvement" and has regained consciousness but still needs round-the-clock care.
"Dawn will always be remembered by us as a gentle soul who was generous to a fault", they said in a statement released by London's Metropolitan Police.
Asked about whether his brother is aware of Ms Sturgess's death, Matthew said Charlie was "very upset".
Meghan Markle and Duchess Kate debut new looks for RAF centenary
Earlier in the day, several members of the royal family attended a service at Westminster Abbey to mark the centenary. Meetings with The President of Ireland, Michael Higgins, and with The Taoiseach, Leo Varadkar, are both planned.
Scotland Yard have confirmed this morning that they have "briefly" spoken to Charlie as they desperately attempt to identify the source of the Novichok.
Britain has blamed Russian Federation for the poisonings, but Moscow has strongly denied any involvement. Basu expressed sorrow for the death of Sturgess, who had three children.
Describing the difficulties of the investigation, Metropolitan Police Assistant Commissioner Neil Basu said: 'There are multiple scenes, there are only limited numbers of scientists and forensic medical officers - all of whom are volunteers by the way - to do what is a really, really unsafe piece of work for obvious reasons.
He said no one else in the Amesbury and Salisbury region, where the couple lived in southwestern England, has shown any sign of Novichok poisoning.
Last week, Sturgess and Rowley were found collapsed at a residential building in Amesbury, Wiltshire, just eight miles north of Salisbury, where the Skripals were poisoned. The search is focused on their homes and a park in Salisbury. Britain has accused the Russian state of the attack on the Skripals, a charge denied by the Kremlin.
He warned the investigation into the latest poisonings would take months.
Chief Medical Officer Dame Sally Davies said people needed to avoid picking up foreign objects "in the interests of their own safety".
Moscow said London has declined its offers for a joint investigation into the poisonings.