One of my professors, so long ago that I can't remember which*, said it was not a who-dun-it but a why-dun-it.

The murder scene itself is so vivid that it's easy to forget that the long middle of the novel is the cat-and-mouse game between him and the detective whose name I forget.

* I think I remembered. Thank you Roman! https://www.dignitymemorial.com/en-ca/obituaries/calgary-ab/...