Suspected poisoners Alexander Petrov and Ruslan Boshirov went to the Czech Republic when Skripal could have been there. The British say they were tracking him – but maybe they were tracking the Novichok nerve agent, which Porton Down and the Czechs had.
The Czech government has refused the claims from Russian sources that it would have produced Novichok. The nerve agent produced in the country was not the same.
Anatoly Chepiga and Aleksandr Mishkin (alleged Ruslan Boshirov and Aleksandr Petrov) visited Czech Republic in 2014 when Skripal was there as well. "It looks like the Russians had a group of people that followed Skripal long before the attempt to assassinate him," the publicly funded Czech radio station quoted one source as saying. See the English rereading of the Czech Radio report here.