The second suspect in the Salisbury poisoning case was a doctor and highly decorated Russian military intelligence officer, an investigative website says.
Bellingcat said it used a combination of online material and leaked documents to identify Alexander Mishkin, 39, as a person linked to the attack in March.
It said President Vladimir Putin had presented him with the Hero of the Russian Federation award in 2014.
When asked about the naming of Dr Mishkin, the Kremlin would not comment.
Last month, Bellingcat named the first suspect as Anatoliy Chepiga, a claim also rejected by Russia, which says it was not prepared to discuss reports or media articles on the case.
At a news conference held in the Houses of Parliament on Tuesday, Bellingcat investigator Cristo Grozev said Dr Mishkin - like Mr Chepiga - was a member of the GRU and given the celebrated award for "actions in Ukraine".
He said Dr Mishkin's grandmother had a photograph that had "been seen by everybody in the village" of President Putin shaking his hand and giving him the award.
The BBC has contacted two people who knew Dr Mishkin as a child in Loyga in the north of Russia, and they confirmed from photographs that he was the man seen in images released by police after the Salisbury attack.
Bellingcat, a UK-based website, said both Dr Mishkin's real passport and the false passport he travelled to the UK on in the name of Alexander Petrov carried the same date of birth.
Outlining in detail how it identified the Salisbury suspect as Dr Mishkin, Bellingcat said it had pieced together his identity using various databases online, including telephone and car insurance records, and later obtained copies of his passport and driving licence.
It also used social media to contact hundreds of people who may have been at a military academy with Dr Mishkin.
Most people did not respond to the inquiry but one, who requested complete anonymity, said they had recognised Dr Mishkin as the suspect who was interviewed under the name of Alexander Petrov by the Russia Today (RT) television channel.
Mr Grozev said: "That person told us everybody from his class, his department, was contacted two weeks ago and told not to talk to the media."
Bellingcat said Dr Mishkin completed his medical studies at a faculty that trains doctors for Russia's naval armed forces and around the same period was recruited by the GRU.
It said he made several trips to Ukraine, including during the 2013-14 unrest.