We'll never know. It's just that simple. I read the Patricia Cornwell book and found it unconvincing, but I doubt this one would be any more convincing. However, my strong belief is that the average person has never heard of the person who was Jack the Ripper. It was just some guy. (And, yes, it was almost certainly a man for a whole list of reasons.) We like to think it must have been someone important, but realistically, it probably wasn't--except in this one particular. And the quality of evidence-gathering from that era precludes a real solution now.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"