I've been having poor luck lately with picking books from this io9 list of the "Top 10 Greatest Science Fiction Detective Novels Of All Time". But—guess what?—this one was pretty good. Written in 1992, it's set in London in the far, far future of… 2013! So part of the fun is checking on how the author, Philip Kerr, envisioned what our world might look like.
(Aside: It's easiest to pick out things he got wrong: for example, 2013 London has lots of poorly-assimilated refugees from the Chinese takeover of Hong Kong. The death penalty has been banned, but criminals are routinely sentenced to "punitive coma", which is much cheaper than inprisonment.)
The book's premise is that enhanced genetic testing has allowed the authorities to detect a "VMN-negative" population, men with a psychological predisposition to violent sociopathy. Nobody wants to lock these people up, but they are entered into a database and provided with shrinks and drugs if they want.
Except one of them, with the codename "Wittgenstein" uses his diagnosis as a springboard to break into the program's database, find the identities of his fellow VMN-negatives, and undertake to murder them, one by one. He also begins to identify with his codename, constructing an elaborate philosophical justification for his actions.
Other than the futuristic premise, the story is a police procedural, following the investigation headed by female detective "Jake" Jakowicz. The narrative is interspersed with excerpts from Wittgenstein's "diary", where he discusses his motives and procedures.
Note to the squeamish: it's all a very sordid business, and Kerr doesn't shrink from explicit description.