Patricia Cornwell wrote a book purporting to solve the question of Jack the Ripper's identity. It's full of logical fallacies and circular logic and demonstrates nothing of value. I read it years ago and I'm still angry about the time I wasted reading it.
If you have two books in one big volume, you probably have something else. Patricia Cornwall's Portrait of a Killer is definitely available in mass market paperback and is only 490 pages even with the photo plates inside. I used to have a copy but decided it wasn't worth keeping and either sold or donated it when I downsized my book collection a few years ago. Here's the Amazon page for it if it helps: https://www.amazon.com/Portrait-Killer-Jack-Ripper-Closed/dp/0425192733
Here is a link. She did one more as well, maybe two. She got obsessed with the case. Spent millions of dollars buying stuff related to the case and the guy she thinks was the killer.
This is true. No disagreement there. Have you read 'Portrait of a Killer...'? (https://www.amazon.com/Portrait-Killer-Jack-Ripper-Closed/dp/0425192733) Very highly recommended if not. I don't entirely agree that its "case closed" as the book claims; however, it provides some great insight into a theory about an artist, and points out some of the discrepancies in the letters.