There are a lot of messed up people in the world. And many stereo types are saying it was North Korea. But it was not. It was just 2 crazy men who enjoy watching people go through hard things. And they might have gone through a tragedy earlier that made them mad. But no one really knows.
Seems to me that the older brother was the ringleader, for whatever reason, it seems he was very angry. The younger brother was following his lead. Hopefully , the younger brother can shed some light on why this happened