This is the first book in a long running series by Steven Havill. I like to start at the beginning as many times a series of books builds upon one another. This is definitely the case as Undersheriff Bill Gastner later becomes sheriff.
His replacement, Estelle Reyes, also later ends up with her own series as the sheriff after Gastner retires (and of course he shows up in most if not all of the later books).
Early in Heartshot
five teens are killed in a tragic car accident, Posadas County Undersheriff Bill Gastner quickly realizes there may be more to the tragedy than first thought when cocaine is found in the wreck.Heartshot Review