In another instalment of its running coverage about the two men London calls the Salisbury poisoning suspects, the open-source investigators claim they managed to "conclusively" establish what they describe as the real identity of Petrov. Amy Kellogg has the story.
The Bellingcat investigative website on Monday said the second suspect responsible for poisoning former Russian spy Sergei Skripal is Dr Alexander Mishkin, a military doctor working for Russian intelligence agency GRU.
The website claims Mishkin traveled from Russian Federation to Salisbury, England, using Alexander Petrov as an alias.
Sergei Skripal, a former colonel in Russia's GRU military intelligence service, and his 33-year-old daughter Yulia were poisoned in March by a liquid form of Novichok, a substance originally developed in the former Soviet Union.
Bellingcat reported last month that the other suspect also traveled under an alias and was a decorated military agent named Anatoliy Chepiga. Sergei Skripal and his daughter Yulia both survived the attack but a woman who later found the poison, which had been hidden in a perfume bottle, wasn't so lucky.
The poisoning of Skripal, a former Russian agent who was convicted of spying for Britain, became a major global incident.
Bellingcat named him as Alexander Yevgenyevich Mishkin, 39, who was charged by Britain last month under the name of Alexander Petrov.
A spokesperson for London's Metropolitan Police said they would not comment on "speculation regarding their identities".
More details about how it uncovered the identity will be revealed on Tuesday, the website says.
Mishkin was said to have made repeated trips to Ukraine and had even stated the GRU headquarters as his home address.
They explained that they went to the small town as tourists and had always wanted to see its tower.
Putin on October 3 said that Skripal was a "scumbag" who had betrayed his country.
Russian President Vladimir Putin, whose government has long denied having any knowledge of the attack, initially claimed that the two men's names "mean nothing to us", then said that they were civilians.
The US Justice Department also charged seven GRU officers in an alleged worldwide hacking rampage that targeted more than 250 athletes, a Pennsylvania-based nuclear energy company, a Swiss chemical laboratory and the chemical weapons watchdog.
Dawn Sturgess, 44, died in June after being exposed to the same weapons-grade nerve agent after it was apparently discarded.