A police vehicle is parked next to crime scene tape, as a tent covers a park bench on which former Russian inteligence officer Sergei Skripal was found unconscious in Salisbury, Britain, March 6, 2018.
The Bellingcat investigative organisation says it has established the identity of an alleged Russian military intelligence officer who was in Britain when a Russian former double agent and his daughter were poisoned with the nerve agent Novichok.
Bellingcat and their investigative partners said it was "unclear" what Sergeev's role may have been in the Skirpals attack.
Russian authorities are now thought to have taken the "unusual measure" of erasing any public records relating to the three agents over the last two months.
Former double agent Skripal and his daughter Yulia were found slumped on a bench in Salisbury in March 2018.
The two other suspects Chepiga and Mishkin arrived on a flight later that afternoon.
Using the cover name Sergey Fedotov, he arrived at Heathrow on March 2 a year ago hours before Alexander Mishkin and Anatoly Chepiga - the two lead suspects in the Salisbury poisoning.
Instead, Bellingat said he somehow got to Rome "using transportation that has yet to be identified by us" then boarded a flight at 3.30pm that day back to Moscow.
Bellingcat was the first to identify the men as Alexander Yevgenyevich Mishkin and Anatoly Chepiga, both of whom worked for Russia's GRU intelligence services.
The Bellingcat announcement comes after Russian news website Fontanka named Fedotov and made the link to the Salisbury attack in March 2018.
Last September, British prosecutors charged two Russians - known by the aliases Alexander Petrov and Ruslan Boshirov - with attempted murder in their absence.
On Monday, Bulgaria said it was investigating a possible link between the Skripal attack and the poisoning of an arms dealer in Sofia in 2015.
This included a trip days before the arms dealer and his son were severely poisoned with a yet-unidentified poison.
This is a breaking news story and will be updated.