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.