FROM HELL has a very extensive section of footnotes for the whole story. After reading the main story, I was even happier to read through all those notes. It's one of the reasons I think of it so highly as a documentary comic book. Alan Moore wasn't trying to pass off his story as some kind of work of his own genius, sans any other sources for his research.
The reason so many stories about Jack the Ripper are so similar (if they're any good) is because they're all based on the same evidence of the crimes.