It could be Polonium again as with Alexander Litvinenko.. Did you know that the cost of the polonium to kill Alexander Litvinenko cost approximately £20m? A sure signal to others not to cross Russia.
People think 'we', as in the west, are above reproach - but I can assure you 'we' are not. We are responsible for millions of deaths in the last 20-30 years alone, with the invasions of Afghanistan, Iraq, Lybia, Syria - we shouldn't have been in ANY of these countries. Not taking into account the sanctions before that, for Iraq alone, killed over one million children before the invasion.
When you understand this you'll then start to understand why some peoples views on the world don't ideologically match with yours.