Bellingcat, who worked with Russian news organisation The Insider, identified the man as Alexander Mishkin, a doctor working for the Russian GRU intelligence service.
As in Boshirov's case, the group also relied upon "multiple open sources" and "testimony from people familiar with the person" in question.
Bellingcat last month identified Mr Boshirov as a colonel in the Russian military intelligence body GRU, whose real name was Anatoliy Chepiga.
"While Aleksandr Mishkin's true persona has an even sparser digital footprint than Anatoly Chepiga's, Bellingcat has been able to establish certain key facts from his background", the October 8 report said.
Mishkin traveled extensively under the name Petrov between 2011 and 2018, including multiple trips to Ukraine and to the self-declared Transnistrian Republic, Bellingcat reported.
British officials said when they charged two Russians last month in the March nerve agent attack on Sergei Skripal and his daughter that they believed Petrov was an assumed name.
"During his medical studies, Mishkin was recruited by the GRU, and by 2010 had relocated to Moscow, where he received his undercover identity - including a second national ID and travel passport - under the alias Aleksandr Petrov", the report said. British authorities said Skripal and his daughter, Yulia, were sickened by a Soviet-made nerve agent.
Sergei Skripal - who sold secrets to MI6 - and his daughter Yulia survived being poisoned with Novichok on 4 March.
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Alexander Mishkin was born on July 13, 1979, in the village of Loyga, in the Archangelsk District in Northern European Russia.
Anatoliy Chepiga AKA Ruslan Boshirov and Alexander Mishkin AKA Alexander Petrov.
Skripal, a former GRU colonel, was convicted of treason in 2006 by a Russian court after being accused of spying for Britain.
There, they allegedly poisoned Skripal, who was a former Russian intelligence officer turned double agent, using a rare chemical nerve agent called Novichok. They said they went to the city to visit its cathedral.
The British government has blamed Russian Federation for the attack.
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.