Bellingcat claims Alexander Miskin, a military doctor working for Russian intelligence, travelled to Salisbury in southern England to target Sergei Skripal, the BBC reports.
On Monday, Bellingcat reported that the real name of "Petrov" is Dr. Alexander Yevgenyevich Mishkin, "a trained military doctor in the employ of the GRU".
Mishkin's military rank is unknown, but Bellingcat estimates he would be either a lieutenant colonel or a full colonel, based on military rank at graduation and his elapsed time of 15 years.
Using this identity, Alexander Petrov, travelled extensively to several European countries including Ukraine and Moldova.
Mishkin trained as a military doctor before joining the GRU, moving to Moscow in 2010, and being assigned the undercover identity of Alexander Petrov, Bellingcat says, citing both public documents and unnamed sources.
Together with another suspect, earlier identified by Bellingcat to be Anatoliy Chepiga, Mishkin travelled to the British town Salisbury in March 2018 and allegedly poisoned former Russian double agent Sergei Skripal and his daughter Yulia.
A second suspect in the poisoning of an ex-Russian spy and his daughter has been named by a British investigative website.
He has served in Chechnya and Ukraine and was made a "Hero of the Russian Federation" in 2014, the website said.
The poisoning of Skripal, a former Russian agent who was convicted of spying for Britain, became a major global incident.
They explained that they went to the small town as tourists and had always wanted to see its tower.
The Skripals survived after a lengthy hospital stay in intensive care.
British officials said the two were poisoned with Novichok, a military-grade chemical weapon that was developed in the Soviet Union, and blamed Putin's government for the attack. But the nerve agent killed a British woman, Dawn Sturgess, and seriously sickened her partner.
A spokesperson for London's Metropolitan Police said they would not comment on "speculation regarding their identities".
Ruslan Boshirov and Alexander Petrov give an interview to the RT news channel.
In its previous reporting, the team already produced evidence that "Alexander Petrov" is not an authentic persona, but an undercover alias for an officer of a Russian security agency.