Lets see first what is it that you want:
Jack the Ripper as the shadowy misterious serial assassin of systematic and brutal character
or
Jack the Ripper as someone who just can´t be caught by natural means, a supernatural presence to punish humanity
I DMed a pair of "Jack the Ripperesque" adventures:
One included a wight with rogue levels (pretty gruesome detail: its forearms had been worn down to "bone blades" which gave some insane climbing bonuses), corpse stealing, and a hidden temple to "Oonvelshar" under a mausoleum in the graveyard.
The other was far more complex, it all started with the clean (not a drop of blood fell from the body) death of Lady Sarina (after a presumed private noble "exotic art critique party" at her home) and a chat with her housekeeper gnome-on-stilts. It included a summoner with a cat familiar, a bound yugoloth in disguise, a cat familiar transmuted into "cat-folk", the stealing of a shadowstuff blooddrinking ceremonial dagger from Lady Sarina's house, the threat of stealing Fiend's Embrace from Lord Arak's collection, and the strange smell of urine at all the crime scenes.
They ended up discovering the lead thanks to a librarian who fed cats who would come to his window (up at the last level of the library), and had noted the absence of a black cat.
The last one was the first adventure in which I required characters to do all the investigation work, a great game... I should write it down someday...
[sorry for the threadjack

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