A second suspect in the Salisbury case has been identified as Alexander Mishkin, the BBC understands.
The Bellingcat investigative website says the man who travelled under the alias Alexander Petrov is a military doctor working for Russian intelligence.
Last month, Bellingcat named the first suspect as Anatoliy Chepiga, a claim rejected by Russia.
Russian ex-spy Sergei Skripal and his daughter Yulia were poisoned in March.
The British open-source website said it had identified the suspect using testimonies from people the suspect knew and a scanned copy of his passport.
It claims he was recruited by Russian intelligence in 2010.
More details about how it uncovered the identity will be revealed on Tuesday, the website says.
A spokesperson for London’s Metropolitan Police said they would not comment on “speculation regarding their identities.”
Sergei Skripal – who sold secrets to MI6 – and his daughter Yulia survived being poisoned with Novichok on 4 March.
The event sparked a series of accusations and denials between the UK and Russian governments, culminating in diplomatic expulsions and international sanctions.
Following the attempted poisoning, UK investigators said one of the two suspects had travelling under the name Ruslan Boshirov.
Speaking on Russian TV last month, that suspect said he was civilian who had visited Salisbury as a tourist.
In September, Bellingcat revealed he was actually an military intelligence officer named Colonel Anatoliy Chepiga.
He has served in Chechnya and Ukraine and was made a “Hero of the Russian Federation” in 2014, the website said.