From Hellblazer

I do not possess copies of Alan Moore's From Hell, having bought them to read and give to my son-in-law. I can borrow his copies, having retrieved them from a former colleague who had had them on long term loan, but a rereading of From Hell will have to wait until after some other reading.  

From Hell has four layers:

the history of the Whitechapel murders;
a particular theory of the murders;
a fictional account of the events and the people involved;
auctorial notes explaining and differentiating history, theory and fiction.

Apparently, Moore wanted to write about a murder, not as an Agatha Christie/Cluedo parlour game but as a human event with real causes and consequences. The Ripper seemed old hat so he considered the case of Buck Ruxton, which is set in my home town of Lancaster. However, the Ripper Centenary came around so suddenly there were a lot of new books and the Ripper's Whitechapel murders were easy to research.

I remember a four issue John Constantine: Hellblazer story called "Royal Blood" as possibly the most horrific fiction that I have ever read. Googling reminds me that it was written by Garth Ennis. Apart from the word "Hell" in their titles, From Hell and this Hellblazer story have two connections:

Alan Moore wrote From Hell and created John Constantine;
both works present the same theory of the Whitechapel murders and Constantine encounters the demon that was in the Ripper.

Why is "Royal Blood" so horrific? I do not have copies to hand. From memory, an agent of the British Establishment shows Constantine a London Club where politicians and celebrities, people we see in the news, relieve the stress of their highly pressured careers by performing horrific acts. Constantine's expert help is needed because a Club member has released and been possessed by the Ripper demon and has fled from the Club. We see panels of the possessed man stalking a victim while trying to remember who he is and remembering that he had a beautiful wife.

When Constantine insists on knowing who he is dealing with, his informant says, more or less, "This is very embarrassing. He is highly respected at home and abroad. He is a very senior member of the Royal Family...", thus ending Part 1, and, for me, the full horror of the story is in that first issue.