Last month Bellingcat said it had identified the first suspect, originally identified under the name Ruslan Boshirov, as Anatoliy Chepiga and obtained leaked files that show Chepiga was deployed to Chechnya three times and included old passport photos of his, which resemble the man British authorities named as Boshirov.
London police said they would not comment on speculation about the real identities of the two men facing charges, in response to a query about the latest Bellingcat report, and repeated they believed the men had used aliases.
Between 2011 and 2018 he travelled extensively under his new identity, Bellingcat said, including making frequent trips to Ukraine.
British prosecutors charged Petrov and another man they named as Ruslan Boshirov in absentia with attempted murder for the Novichok nerve agent attack on Skripal and his daughter in the English city of Salisbury in March, but said they believed the suspects had used aliases to enter Britain. The Kremlin has maintained variously that the Skripal poisoning never happened, that it was carried out by the British spies in order to blame Russian Federation or that murky third parties were responsible.
The Skripals survived after a lengthy hospital stay in intensive care.
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.
He was recruited by the GRU while at one of Russia's military medical academies, eventually becoming a military doctor.
President Putin's spokesman Dmitry Peskov said the Kremlin was not prepared to discuss investigative reports and media articles on the poisoning of Mr Skripal, and complained the British authorities had refused a Russian request to share details of their inquiries. The authenticity and veracity of the documents, which Bellingcat claimed it got from a Russian database, could not be immediately verified.
They were then able to show that Mishkin, with the same date of birth as his cover identity, had registered his vehicle to the address of the GRU's main headquarters building in Moscow.
Higgins noted that Mishkin's home village is snowbound for much of the year.
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 U.S. Department of Justice indicted seven named GRU officers on charges they had hacked worldwide organizations, including the Organization for the Prohibition of Chemical Weapons (OPCW).
The US Justice Department also charged seven GRU officers in an alleged global hacking rampage that targeted more than 250 athletes, a Pennsylvania-based nuclear energy company, a Swiss chemical laboratory and the chemical weapons watchdog.
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.