A British man exposed to Novichok, four months after the same nerve agent was used against a former Russian spy nearby, had found it in a perfume bottle, his brother said.
The toxic nerve agent, Novichok killed 44-year-old Dawn Sturgess on Sunday, and left her partner, 45-year-old Mr Rowley critically ill.
Mr Rowley's condition continues to improve in hospital, but Ms Sturgess - a mother of three - died just over a week after being poisoned by the deadly nerve agent.
The vessel found in Rowle's house cointained the lethal substance produced in the Soviet Union during the Cold War, scientists confirmed.
Matthew Rowley told the BBC that his brother Charlie, who is seriously ill in hospital, said he had picked up the perfume bottle containing the chemical weapon.
About 400 items have been recovered by police investigating the Novichok poisoning of a couple in Wiltshire.
Detectives said they were still trying to find out where the bottle came from, and why it ended up in the house.
The police said further testing was trying to establish whether the substance that affected Rowley and Sturgess was from the same batch as was used against the Skripals. The couple were identified with symptoms similar to those observed in ex-GRU officer Sergei Skripal and his daughter Julia, is poisoned in Salisbury in March of this year.
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Investigators have spoken to Mr Rowley and will speak to him again in a bid to find out how he and his partner were poisoned.
Wiltshire Chief Constable Kier Pritchard welcomed the development, describing it as "significant and encouraging".
Neil Basu, the head of UK Counter Terrorism Policing, said there is no guarantee that all of the substance has been found. Search cordons remain in place.
The Foreign Office also on Friday said it had invited independent technical experts from the global chemical weapons watchdog to Britain early next week "to independently confirm the identity of the nerve agent".
Officials say: "If you didn't drop it, then don't pick it up".
Britain has blamed the attack on the Russian Government; Moscow vehemently denies responsibility.
Public Health England has advised citizens not to pick up odd items made from glass, metal or plastic.