However, Professor Leonid Rink told the RIA news agency that the attack did not look like Moscow's work because Sergei and Yulia Skripal had not died immediately.
The Skripals remained alive but in critical condition more than three weeks after they were found unconscious in the English cathedral town of Salisbury. A policeman who helped them is also in hospital in a serious condition.
Rink said he worked under the Soviet Union at a chemical weapons facility where the Novichok military-grade nerve agent was developed. Asked if he was one of Novichok's creators, he told RIA: "Yes. It was the basis for my doctoral dissertation."
Echoing a theory floated in Russian state media, Rink said the British could have been behind the attack.
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