Former Russian spy Sergei Skripal worked for the intelligence of four NATO countries until 2017. German Focus reported this with a reference to a high-ranking source in the counterintelligence of Alliance.
In 2012, Skripal together with representatives of MI6 went to Prague, where was telling the local intelligence how Russian spy network works.
The source claimed that in summer 2016, the former Russian spy provided data to Estonian intelligence necessary to expose three Russian spies worked in Tallinn.
Also, there is information that Skripal informed Spanish intelligence about the activity of Russian mafia in the country.
Reportedly, Skripal was detained in 2004 for working for British MI6, in 2010, he was released on the exchange of agents. After, he was living in the south of England.
As it was reported Sergei Skripal and his daughter Yulia were poisoned in British Salisbury. Later, Theresa May, British PM, stated that Russia was responsible for that, and the investigation has confirmed the use of the Novichok nerve agent, which is produced in Russia.