"In fact it was the drugs that were making the children ill and the children had been enrolled on the secret trials without their relatives' or guardians' knowledge."
Read on: http://news.bbc.co.uk/1/hi/programmes/this_world/4038375.stm
Yes, there's a common theme here, all right. The question is "why?" Because people think that they can get away with it? I suppose that if one wishes to find out what people are capable of, one has to put them in a position where they believe that there will be no repercussions from their conduct, irrespective of how low the motivation was for that conduct.