Dick Hickock is Perry's crime partner, characterized by his blond hair, blue eyes, and lean build. His outwardly normal appearance contrasts with his life of crime, which he rationalizes as separate from his personality.

Al Dewey is the lead detective on the Clutter case representing the Kansas Bureau of Investigation. A family man with a background as a sheriff and FBI agent, he becomes deeply committed to solving the crime.

Herbert Clutter is the owner of River Valley Farm, a respected figure in the Holcomb community, known for his disciplined life and fair treatment of employees. He is the husband to Bonnie and father to four children.

Bonnie Clutter is the wife of Herbert Clutter and mother to their four children. She struggles with her mental health but is deeply religious and has found solace in short-term work outside the home.

Nancy is the Clutters’ youngest daughter, a bright and active 16-year-old. She is admired in her community for her academic excellence, domestic skills, and warm personality.

Kenyon is the Clutters’ only son, a reserved 15-year-old with a tall, lanky build. He enjoys building and inventing, and is close to his family despite his quiet nature.

Sue Kidwell is a close friend of Nancy Clutter, known for her sensitivity and artistic aspirations. She comes from a smaller family background and is impacted by Nancy's influence.

Bobby Rupp is Nancy Clutter's boyfriend of several years, who shares a long history with the Clutter family. Despite differences in religious backgrounds, he is considered a suspect early in the investigation.

While on Death Row, Perry and Dick share the space with other inmates, including Andy, who is noted for his significant presence and complex background. The dynamics among the inmates mirror Perry and Dick's partnership.

Floyd Wells, a fellow inmate and former work associate of the Clutters, inadvertently provides key information about the Clutter family that leads to the investigation of Dick's involvement in the crime.