Rhetorical questions are questions posed which are not meant to be answered. They are used to introduce new subjects or problems.
Who was responsible for the genocide? That depends on how the diary entries are interpreted.
Rhetorical questions are useful to introduce ideas. For example:
Sir Edmund Hillary is credited for being the first man to conquer Mount Everest. But, who did reach the summit first? Some believe that Englishman George Mallory, who led an expedition to Everest in 1924, reached the summit first. However, Mallory died on the mountain, and it is unknown whether he reached the top.
Glossary of grammatical terms