Don't you mind sharing what country are you from, by the way?
It sound rather something out of a nadie movie. I don't even know why should anyone would go and use poisoned food instead guns, people would realize what happened anyways, eventually.
As you said, it all dependent on his country and the cultural background. I can say that it is a timid way to kill and if people have been dying through that means, I bet no one will eat during occasions and many people would have died more than recorded.
They died and no autopsy conducted?
There is a chance that someone with enough power could have intimidated or bribed the morgue so they would forge the cause of death. It is something that has happened before. Even though all this sounds a little bit dramatic and unrealistic, I would not go further and claim that OP is lying, the world we live in is too big and on internet we can find all kinds of people, with all kinds of family members and political links.
Anyways, the point OP is trying to establish may be accepted by some and rejected by others, depending on culture and out personal experiences with our local politics. It is very relative.