Well, I certainly agree with you on your Level 2 and Lizzie Borden. Myself, I've always pictured Lizzie naked, lying in wait to do in Mom and Dad. But that probably says more about me than it does about Lizzie.
Its seems like you feel JtR belongs in #3, rather than in my opinion, a #4 on the scale.
Identifying people known at the time to be of a character type that would fit a serial killer profile....which is in this case itself was bound to 5 set victims of the period by the majority of contemporary opinion,.. are not in my opinion valid "suspects" at all. I think that also applies to "suspects" named in memorandums, book notes, private letters or conversations among investigators and reporters.
Isnt the real truth here that not one person that we call "suspect" here has any evidence or investigative clues that would suggest they committed the 5 crimes alleged to have been by Jacks hand?
For me thats the oddity of this study....sound researchers and historians and criminologists assess the viability of suspects compiled... based on little more than their known character flaws and known criminal behavior...not always violent in nature.
I suppose thats a bit blasphemous in Ripperology, the entity that feeds off those "suspected" men.....but without intending disrespect to anyone, we really have no right to call literally every man suggested as a possibility as a "suspect".
In this study, "suspect" is just someone with access to the women and knowledge of the area, we have no idea whether the illness that the killer had manifested itself in prior crimes or violent behaviors before the murders.....in which case the list of "possibles" could be pages in length.
My personal opinion is that the term "suspect" in these cases is misleading.
Location: McWopetaz Metroplex, Illinois U. S. of A.
It initially surprised me that Level 4 was the tier where I had the most difficulty coming up with examples. I guess there aren't that many cases where the investigators don't at least have a person or persons of interest. Before, I hadn't given it any thought.
This my opinion and to the best of my knowledge, that is, if I'm not joking.
Level 1: Cases where there is a standing conviction but some doubt about it (James Hanratty) or cases where there is no conviction but where there is little doubt regarding the perpetrator (Bella Kiss).
Hanratty I'm still arguing about (and probably will until I go tits up), but would you include Hauptmann in your Level 1? For ages I thought Hauptmann had been stitched up, but now I'm not so sure. As little seems to have been written recently about the Lindberg Kidnap Case, what's the current thinking in the USA?