Monsters of the 20th century reading list

I’ve been reading books about the great monsters of the 20th century- Real monsters. So far my list looks like this:
Stalin: Court of the red Tsar, Koba the dread
Kim Il Sung: Under the loving care of the fatherly leader
Pol Pot: Pol Pot: Anatony of a nightmare, First they killed my father
Mao: Mao, A life (as yet unread)
I figure I should include a book on the Imperial Japanese junta that was in charge during WWII, but so far haven’t found anything so specific, but I bought
Hirohito and the making of modern Japan. (as yet unread)

I’ve been looking for something on Idi Amin, but have not been successful.
I also need Hitler, of course, but I’ve been leaving him for last.

I would appreciate suggestions on additions to the list, or books that should be included.
Thanks!

I would suggest We Wish to Inform You That Tomorrow We Will be Killed With Our Families by Philip Gourevitch. This was a very hard book for me to read, but it is very well-written and compelling.