I always thought the heat was the driver. There has historically been more crime in the summer than in the winter, for example. Heat makes you do crazy things, as some noir novel probably said.
I guess it'd be nice to have some research to try and find out the real reason and challenge our own hypothesis, rather than always fall back on "I thought X was the reason". This is why the defunding of these programs is so frustrating, because especially around the social sciences, Americans tend to value their own gut rather than empirical studies.
This assumes that the research was finding the real reason and not just finding evidence for the researcher's gut reasoning.
It's a short story and not a novel, but there's the short story August Heat[0]; it's available at [1].