Help me with this!!!

Who really killed Sidney Cromwell? 'Dear Diary' from Wattpad(app name)
I really can't read till the end to know cuz I'm really in hurry and I must give the assignment to my teacher on MONDAY. I was just at chapter-4 and the book is up to 48 chapters. I can't read that fast so hope people who had read that book help me with it. Oh and this is the book cover just to make sure not to get wrong.