The murder of Bosch's mother has been mentioned in many books that I have read. I think the stories in the tv series are written new. I just started season 3.

This was thoroughly discussed on the old IMDb discussion boards. Oh how I miss them at times like these! I do remember that so far each season has basically combined the plots of two books, with the solving of his mother's murder throwing in a third (IIRC).

This is from Wikipedia: A third season, which adapts Connelly's novel The Black Echo and elements of A Darkness More Than Night, premiered on April 21, 2017.

@imdb.com said:

Really enjoyed the season, but wish there were more episodes. Anyone know what book each season is based off?

https://harrybosch.fandom.com/wiki/Category:Seasons