The Bellingcat report says Mishkin, the doctor it said works for Russian intelligence, was born in 1979 in the Archangelsk District in northern Russia and graduated from the elite Military Medical Academies, where he was trained for medical work in the Russian navy.
But investigative journalism site Bellingcat has dug into the backgrounds of "Petrov" and "Boshirov", and says it has identified both men's true identities and that they work for the GRU.
However officials are not disputing Bellingcat's identification of the men.
In an interview with Margarita Simonyan, editor-in-chief of Russian TV outlet RT, the men confirmed they were the people identified by the United Kingdom investigators but claimed they were coincidentally in Salisbury at the time as tourists.
"We have now identified "Alexander Petrov" to be in fact Dr. Alexander Yevgenyevich Mishkin, a trained military doctor in the employ of the GRU", the British-based group said in a report published on its website.
The two men accused of the attempted assassination of ex-Russian spy Sergei Skripal were originally named by the United Kingdom authorities as Ruslan Boshirov and Alexander Petrov - although it was made clear that the names were aliases. They said they had discovered passport information linked to the men's aliases that showed extensive travel, as well as ties to the Russian security services. They have both since been discharged from the hospital.
Chepiga was also awarded the Hero of the Russian Federation award by President Vladimir Putin in 2014, receiving a luxury Moscow flat at the same time. Only a few officers each year receive the award, which is typically given personally by President Vladimir Putin.
They have cited a photo showing the Russian president to shake her hand and exhibited by the grand-mother of the suspect to the inhabitants of the village of Loyga, in the north of Russia, where he grew up.
Trump apologises to Kavanaugh over 'unfair' treatment
On Monday, the president said "evil" people brought about the situation that slowed Kavanaugh's confirmation. "False charges. Democrats have said that an FBI investigation into the allegations that Trump ordered was too limited in scope to be useful.
Kanye West has a awful iPhone passcode
The 41-year-old music star also mused about why Democratic candidate Hillary Clinton lost the presidential election in 2016. He started showing that he actually had power, he wasn't just one of a monolithic voice, that he could wrap people around.
Peyton Manning jokingly shames Drew Brees for breaking his passing record
Behind three touchdowns from Brees, New Orleans cruised to a 43-19 win over the Washington Redskins . Drew Brees knocked Peyton Manning into second place on the NFL's all-time passing leaderboard.
The website said it had identified Petrov using testimonies from people the suspect knew and a scanned copy of his passport.
During his studies he 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 Alexander Petrov, it added.
Bellingcat founder Eliot Higgins and researcher Christo Grozev told reporters at an event in the British parliament that they discovered Mishkin had taken part in covert operations in Ukraine and the breakaway republic of Transnistria.
The Press Association has confirmed the investigation is looking at several suspects, with a senior government source stating that there are "at least two". After the attack, new sanctions were imposed on Russia and about 150 Russian diplomats were expelled from Western nations.
The man, from Russia's military intelligence service the GRU, was reported to have visited Salisbury ahead of the poisoning of Sergei Skripal and his daughter Yulia, according to The Daily Telegraph.
The poisoning of Skripal, a former Russian agent who was convicted of spying for Britain, became a major global incident.
The group also said that until 2014, Mishkin's registered home address in Moscow was the same as the GRU's headquarters. Yulia has since issued a written statement and appeared once on camera, saying she hoped to one day return to Russian Federation.
The Skripals were sickened by Novichok, a Soviet-made nerve agent. One of them, Dawn Sturgess, died.