Well I meant that, whatever substance is the cause, if it was intentionally introduced, then someone had to know in advance it would be harmful and at the same

Well I meant that, whatever substance is the cause, if it was intentionally introduced, then someone had to know in advance it would be harmful and at the same time it couldn't be common knowledge or it would have been banned. If that's what happened, then how can the accusation hold? How would anybody prove it?