What, if the intentionally "signature" is, that there is no signature of certain repeating signs and exactly that is the reason for not being caught for years? Okay, he has to be very ill in his head (!!), but he might be so clever to work out a plan of which "signatures" his next crime will exhibit. He pretends to have the needs doing it, in real he hasn't these needs but fabricates the "big show" for the investigators. Delphi these "signatures", Evansdale those "signatures", another crime scene again different. If he is a crime fanatic, he has studied all the subtleties and keeps doing it. He is playing a giant game with authorities and is able to completely fade out his victims. His victims for him are only: exact dates/exact times/preferred locations/different MO/different signatures. Names wouldn't play a role, age perhaps neither.
I can't always use the word "perhaps" or "possibly", but: it's only my opinion atm, how the perp might think and "work". MOO
But what you are talking about is a giant collector. He is not playing with LE.
He is collecting own crime.
But within this crime, he would be collecting subsections, so to say.
Imagine any collector. Imagine it is a woman, and she’s collecting diamonds. Different cuts, shapes, times, rings, necklaces, bracelets, but diamonds it will be. Or pearls. It could be Tahitian, South Sea, Japanese, but still pearls.
Or books. It could be a unifying theme, time period, genre, or first editions, or even covers, but there are some other principles.
Ask gun collectors, as I don’t collect guns. I collect clothes, there should be something matching.
And collections are organized.
What I want to say, the person would introduce himself as a “collector of books”, but inside, there would be other groups.
There should be some subdivisions of his murder collection. They are not totally random.
I would put all known murders into a computer and see what else pops out. Could be dates, could be gender, could still be something in the places. So we shall know what his “subsections” are. Letters? D - Delphi, E - Evansdale.
Lastly, do you think his gait is different? DC thinks, no, other people think, yes. At least there is some locality in his accent. Let us say, Midwest could be his lair. He won’t move to the area where he’d stand out. So he travels, but it would be within a certain areal. Where he blends in. If he stands out in certain ways, he can’t afford to be noticeable.
Lastly, maybe there are communities of people who show “collections” online, people want to boast.