I’d like to read about the development of the state after the fall of the Roman Empire in the west and what their idea of justice entailed and how they enforced it
It might not be exactly what you're looking for but funnily enough I just picked up a book titled 'The Medieval Underworld - Andrew Mccall'
The Medieval Underworld is a 1972 illustrated book authored by Andrew McCall, published by Barnes & Noble Books in New York. It details the basis for criminal and ecclesiastical justice from the fall of Rome to about 1500.
Thought it sounded interesting so I got it, though I have only skimmed it thus far so cannot say how well it would fit your criteria. The chapters are: