longtime ally russia. >> translator: the american side can't not understand that the syrian government troops did not use chemical weapons there. >> reporter: it's a pattern russia has been linked directly and indirectly to chemical 2004 ukraine's prowestern presidential candidate victor lukashenko suffers a mysterious and potential poisoning. it utterly changes his face and again raises the specter of russian involvement. >> translator: i had never felt anything like it before. >> reporter: 2006, a former kgb officer working with british intelligence drinks tea laced with radioactive polonium. he dies in london. authorities say russian agents were to blame. 2018, sergei scripal, a former russian military officer and his daughter are poisoned in england.