You have so many to make up your mind. Since Jack the Ripper in 1888, sadistic killers have make their point. All serial killers have that sadistic touch within them.
Take for example Mary Bell. A quite little girl that killed two boys for curosity. The story tell you she was a wicked child.
Then you jump to the Jefrey Damhner story wich has a horrific descriptions on cuting men as cattle.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.