Anna Chapman condemned Britain’s response to the nerve agent attack, which has left the 66-year-old and his daughter Yulia Skripal in a critical condition.
“As always Russia is guilty by default… despite the fact that traitor Skripal was pardoned by the President and released,” the 36-year-old, who now works as a model and television presenter, wrote on Instagram.
“When investigating any murder, the first issue is the motive of the crime. Who benefits from it? In any case, Russia is definitely not interested in such scandal. Does the West need proof to blame Russia?”
Ms Chapman, who married to a British trainee psychologist, was allegedly part of a Russian spy ring in the US known as the “Illegals Program”.
She pleaded guilty to conspiracy to act as an unlawful agent of a foreign government and was among ten “sleeper” agents returned to Russia in 2010.
They were exchanged for four double agents, including Mr Skripal, who was given refuge in the UK having passing intelligence to MI6 during his time as a GRU military intelligence agent.
Mr Skripal and his 33-year-old daughter were found slumped on a bench in Salisbury city centre after being exposed to a nerve agent on Sunday.
They remain seriously ill in intensive care and a police officer who was among the first to respond to the incident is also in hospital.
Suspicion has turned to the Russian government, which jailed Mr Skripal for “treason” in 2006, or former spies he betrayed as a double agent.
Security sources told The Independent that he was no longer an active MI6 asset, but may have become a target by attempting to “freelance” for private intelligence companies run by former spies.
Investigators are looking at the possibility that he was poisoned at his Salisbury home, possibly by the nerve agent being delivered in a package that Mr Skripal unknowingly opened in his daughter’s presence.
They are also understood to be reviewing the deaths of his wife, in 2012, and son last year, which were originally thought to be of natural causes.
Parallels have been drawn between the attack and the assassination of Alexander Litvinenko, a former officer with Russia’s Federal Security Service (FSB) who was poisoned with radioactive polonium at a London hotel in 2006.
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Ministers have declined to say who is believed to be responsible in the wake of high-level Cobra and National Security Council meetings, but threatened further sanctions against Russia if state involvement is found.
Tobias Ellwood, a defence minister, said the Government was discussing its response to the “clandestine and sinister attack” with Nato allies.
“We will respond with the full force of the United Kingdom’s resources if that is the appropriate and proportionate thing to do,” he said.
Following a meeting of the Government’s Cobra emergency committee on Saturday, Amber Rudd revealed that the investigation had widened to involve 250 counter-terrorism police officers, as well as military personnel.
Police have now identified more than 240 witnesses and are examining at least 200 pieces of evidence.
Chemical weapons specialists, Royal Marines, RAF and Army troops remain in Salisbury to remove vehicles and other items that were possibly contaminated for further investigation.
The Russian government has vehemently denied involvement in the attack and accused British authorities and media outlets of “pure propaganda”.