It is a strength of the novel to keep the reader guessing about Luke. Luke's own father harbored doubts; he asked Falk if Luke had killed before. The rabbit scene early on also suggested possible psychopathy, but as someone above mentioned, what if the rabbit really did "just die." Luke's parents asked Falk to look into the murders, not knowing what he would find, but not wanting to believe that Luke could kill his own wife and child. Luke differs from Grant Dow in that Luke had a normal childhood and grew up with loving parents who modeled a good marriage. Dow, on the other hand, had a terrible role model in his murderous uncle. Dow is genuinely mean; Luke strikes me as untrustworthy and dark, but not as inherently evil as Dow strikes me. People thought Luke could have killed because they knew he had temper, they thought that the drought and the incessant heat made him snap, and quite frankly, they didn't see a need to look elsewhere for a suspect once Luke's body was found and it looked as if he had committed suicide. The author is masterful in keeping us guessing by presenting all sides of Luke and various people's opinions of Luke. It wasn't until Falk and Raco began to look at things from a different light that what really happened fell into place.