The organization added that The Insider, Bellingcat's investigative partner in Russia, sent a reporter to the northern Russian village of Loyga, where at least seven people recognized photos of the man identified initially as Petrov as "our local boy" Mishkin.
Investigative group Bellingcat on Monday identified the second suspect in the poisoning of former Russian spy Sergei Skripal as a doctor employed by Moscow's GRU military intelligence service.
The identification of Mishkin is a further embarrassment for the GRU after the British and Dutch authorities last week exposed its failed attempt to hack the computers of the Organisation for the Prohibition of Chemical Weapons, which was helping to identify the nerve agent used against the Skripals.
The Skripals survived after a lengthy hospital stay in intensive care. Moscow, which denies involvement in the poisoning, declined to comment. The two men had previously claimed to be Alexander Petrov and Ruslan Boshirov, sports nutritionists with a passion for gothic-style cathedrals.
The website said it discovered Mishkin's real identity after obtaining a scanned copy of his passport.
Until September 2014 his home address was registered as the Moscow headquarters of the GRU. The town is exceptionally remote, inaccessible by road except in winter when the grounds freezes hard and normally reachable only by a narrow-gauge railway.
In 2014, he was active in military operations in eastern Ukraine, where pro-Russia separatists lead a violent breakaway movement.
Bellingcat said it used a combination of online material and leaked documents to identify Alexander Mishkin, 39, as someone linked to the attack in March.
A spokesman for the Home Office said "we are not commenting as this is still a police investigation". But the latest revelations seemed to once again undercut Russia's denial that it was involved in the Salisbury poisonings.
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According to a new report released by Bellingcat, Dr Alexander Yevgenyevich Mishkin was handed a Hero of Russian Federation award in late 2014 for his service in Ukraine, where Mr Putin's troops are accused of backing pro-Moscow rebels fighting government forces.
Bellingcat said their findings revealed those claims as false, and proved conclusively that the two men were tied to the GRU.
Unlike the case of Anatoliy Chepiga, "Petrov"'s cover identity retained most of the biographical characteristics of the authentic Mishkin - such as the exact birth date, first and patronymic name, and first names of his parents.
Police officers stand outside the house of former Russian double agent Sergei Skripal in Salisbury, England, March 6, 2018.
It's being reported that one of the Russian spies who poisoned Sergei Skripal and his daughter, Yulia, was a doctor who'd been personally honoured by President Putin.
"While Alexander Mishkin's true persona has an even sparser digital footprint than Anatoliy Chepiga's, Bellingcat has been able to establish certain key facts from his background", Bellingcat said.
Despite the Bellingcat investigation appearing to have exposed the GRU, British security minister has warned against underestimating the threat of Russian Federation.
Last week, the Justice Department filed criminal charges against seven members of the GRU, accusing them of hacking into the U.S. Anti-Doping Agency in Colorado Springs, Colorado, as well as four worldwide sports governing bodies.
Russia's foreign minister Sergey Lavrov has dismissed the allegations, saying the men who were expelled from Holland had been there on a "routine" assignment to provide cybersecurity support for Russia's embassy.