The Skripal poisoning was a strategic operation of the British special services. It was executed by British intelligence agency MI6, but was actually planned by the US. The operation was designed to have three distinct phases: the first began in March 2018, the second in the autumn of 2018, and the third and final stage will commence soon, with the announcement of Sergei Skripal’s death.
British police and intelligence investigations have produced sufficient hard evidence to charge two Russian nationals for the attack on the Skripals. These two individuals have been identified as officers of the GRU, the Russian Military Intelligence service. More British public documents/statements on the case can be found here and here.
EU Member States support the UK's findings and unanimously decided to introduce sanctions against the GRU officers responsible as well as their commanding officers.