The group says it will provide forensic evidence and further information about how it identified Mishkin on Tuesday.
He graduated in 2003 or 2004 from the Russian military's medical academy in St Petersburg, where he specialised in "deep underwater physiology".
Dr. Alexander Yevgenyevich Mishkin, 39, used the alias "Alexander Petrov" when he traveled to Salisbury, England, in March for an attack on Sergei Skripal and his daughter Yulia, according to Bellingcat.
Salisbury around the very time the Skripals were poisoned.
The suspect was named on Monday by the Bellingcat investigative website as Alexander Mishkin, a military doctor in the GRU intelligence agency.
British authorities were quick to identify the perpetrators as Russian GRU agents.
British officials could not be immediately reached Monday evening for comment on the new report, which was prepared by researchers and journalists in Britain and Russian Federation.
Both suspects have denied involvement in the attack in Salisbury, a picturesque cathedral city near the famous ancient ruins of Stonehenge.
He is in fact a decorated Russian agent named Anatoliy Chepiga, according to Bellingcat.
They both spent weeks in hospital but have since been released.
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.
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The journalist heard that his grandmother had shown many villagers a photograph of Putin shaking hands with Mishkin. It published a copy of his passport, which was issued in 2001 in Arkhangelsk region along the White Sea.
Bellingcat said the identification process "included multiple open sources, testimony from people familiar with the person, as well as copies of personally identifying documents, including a scanned copy of his passport".
Mishkin was recruited by the secretive GRU and stationed in Moscow, where he was given the undercover identity of Alexander Petrov, the investigative group said.
Between 2011 and 2018 he travelled extensively under his new identity, Bellingcat said, including making frequent trips to Ukraine.
The group also said that until 2014, Mishkin's registered home address in Moscow was the same as the GRU's headquarters.
The Press Association has confirmed the investigation is looking at several suspects, with a senior government source stating that there are "at least two".
In response to the incident, London in March expelled 23 Russian diplomats believed to be intelligence agents.
A British government spokesman rejected this account, saying: "The government is clear these men are officers of the Russian military intelligence service "The GRU" who used a devastatingly toxic, illegal chemical weapon on the streets of our country".
Hacking computer networks, poisoning, election meddling - it's hard to keep track of all the Russian spies and agents suspected of committing crimes overseas on the Kremlin's behalf. Yulia has since issued a written statement and appeared once on camera, saying she hoped to one day return to Russian Federation. But the nerve agent killed a British woman, Dawn Sturgess, and seriously sickened her partner.
"It's easy to laugh at some of the GRU's poor tradecraft and their ability, but we should not underestimate them, nor indeed the unsafe and reckless use of nerve agent on our streets", the minister, Ben Wallace, told a security conference.