Do you have to know what happened and why? Or, are you happy speculating on the possibilities, wondering about the mystery and never knowing for sure? If you're the first person, you'll hate this book. The second, you'll enjoy yourself.
There is no resolution to the mystery, King does not tell us who killed the Colorado Kid and how. Instead he invites you to pull up a chair and chat with a few friends about a death that may or may not be an unsolved murder. All the known details are presented and you're left to draw your own conclusions. As for what really happened, you'll never know. That's not really the point of the story anyway.