If you are not already familiar with Dell Shannon, please take my highest recommendation for police procedurals with character and humor. Alter egos: Lesley Egan, Elizabeth Linington (real name). She has series under each name, as well as quality historical novels under Linington.
Dell Shannon's primary character is Luis Mendoza, a Los Angeles police lieutenant who grew up poor, became a gambler to survive, joined the police, then unexpectedly inherited wealth from his miser grandfather.
This is one of her earlier ones (1963), about a boy whose great interest in everything his neighbors have and do leads to his death.