Inspector Imanishi Investigates

A 1961 novel by Japanese mystery writer Seicho Matsumoto. The eponymous police officer begins investigating the murder of an unknown man found on the railroad tracks, and starting with almost no clues, he travels around Japan to make sense of the crime and find the killer. The novel also centers on a group of trendy young artists called the Nouveau Circle, who seem to have some connection to the murder.

Tropes used in Inspector Imanishi Investigates include:

Asshole Victim: Deliberately inverted. The murder victim turns out to have been a kind, philanthropic man loved by all who knew him. Thus, the mystery is both a question of "who killed him" and "why would anyone kill him".
Conveniently Unverifiable Cover Story: It turns out that the name/identity by which the murder was known was not his real one, but rather the result of taking advantage of one of these. Specifically, his supposed parents were a couple killed in a bombing raid in Osaka at the very end of World War Two, and he falsified records so that he would seem to be their son.
Determinator: Imanishi essentially becomes completely devoted to pursuing one case and starts with little to no evidence, but eventually finds enough to catch the killer.
Musical Assassin: A realistic take on this is the solution to some of the other murders.
Never One Murder: Played straight, but except for the one that starts the plot going, all deaths seem to be from accidents or natural causes.
Never Suicide: Subverted; it actually is.
Older Hero vs. Younger Villain
Reactionary Fantasy: In this novel and apparently in others by Matsumoto, there's a fair amount of generational conflict, and the older generation is on the detective's side. The older generation are those who were young men and women right after World War Two and when they were young rebels, they did so with idealistic motives. In contrast, the new generation of young rebels are selfish and devoted to True Art Is Incomprehensible.
Tohoku Regional Accent: Plays a big part in the plot, as those who saw the victim before his death recollected the distinctive Zu Zu sound, and Imanishi tries to find the victim's identity based on that accent.