"Mr. Skripal and his daughter were poisoned with a military-grade nerve agent of a type developed by Russian Federation", specifically from the Novichok group, British Prime Minister Theresa May said after the incident, based on an assessment by British experts.
National security adviser Sir Mark Sedwill said cyber specialists from the GRU - Russian military intelligence - targeted Yulia Skripal's email accounts as far back as 2013.
Sedwill said Russia's chemical weapons programme had continued after the collapse of the Soviet Union, and that by 1993, when Russia signed the Chemical Weapons Convention, it was "likely that some Novichoks had passed acceptance testing, allowing their use by the Russian military".
Sedwill's letter to the North Atlantic Treaty Organisation chief detailed the grounds on which British authorities hold Russian Federation responsible of a suspected nerve agent attack targeting Skripal and his daughter Yulia in Salisbury six weeks ago.
Sedwill also said that Russian Federation has tested means of delivering chemical agents "including by application to door handles", pointing out that the highest concentration of the chemical found after the attack was on Skripal's front door handle.
"If somebody was spying, why were the British services not complaining about it, because they always complain if something goes wrong in their country or somewhere else", he said during a news conference in London.
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The codeword for the offensive chemical weapons programme (of which Novichoks were one part) was FOLIANT.
Scientists from the Organization for the Prohibition of Chemical Weapons (OPWC) confirmed Thursday that Novichok was used in Salisbury, England in the attack on Skripal.
He said only Russian Federation had the "technical means, operational experience and the motive" for the attack.
'It is highly likely that the Russian intelligence services view at least some of its defectors as legitimate targets for assassination.Only Russia has the technical means, operational experience and the motive for the Salisbury attack, ' he added. "Within the last decade, Russian Federation has produced and stockpiled small quantities of Novichoks under the same program".
Meanwhile, Russia's ambassador has accused the British authorities of destroying evidence in the Salisbury nerve agent attack. He also questioned the authenticity of a statement issued by Ms Skripal through the Metropolitan Police saying she did not want to meet Russian officials. We have every reason to see such actions as the abduction of two Russian nationals.