If I'm the author, I would defend this large cast by saying, "Exactly! Small towns are incestuous and everyone knows everyone else, but do they really? Because any one of those people could be the serial killer." But listen, I'm just telling you, half the fun of reading a mystery is being able to untangle who the bad guy might be, and that's difficult to do when most of your energy is consumed by needing to create an Excel spreadsheet to keep the characters in line.
Maybe another factor in the challenge of reading it was because the first person narrator was distant from the action. He wasn't a cop or a detective, but rather a high school teacher. It took me a couple of chapters to figure out his job or role in the town and then it was odd that he seemed omniscient. In the re-telling of the story, he recounted entire conversations and thoughts and descriptions of scenes where he wasn't present. You can also chalk this up to the writer's understanding that the reader comes to a novel with a willing suspension of disbelief, but maybe it would've been nice to have some kind of gesture toward explaining how he was able to get these details so precisely, like possibly if he were a reporter for the newspaper.
And then there's this other thing that I don't love--when writers take on a marginalized identity to narrate the story. Like, when a 50 year old white guy writes in the voice of a 22 year old or takes on the persona of a Native American. In this case, the narrator is a gay man who talks about prejudice and how the police are targeting other gay men in the town. But then, the killer turns out to be a perverted man who is not comfortable with his sexuality and has had sex with the male albino in town. So, like, if you're writing a story and pointing out that society is prejudiced against homosexuality, perhaps don't then have the madman turn out to be a guy who cuts off the hands of girls because they're dirty and who is desperately ashamed of his own desires. Lest you think I'm making assumptions about the writer, I'd just like to point out that the back cover of the book jacket reads something like, "Stephen lives in Syracuse with his WIFE and TWO CHILDREN." In other words, HE HIMSELF IS NOT GAY, in case you were wondering.