Herb Clutter was a prosperous farmer in western Kansas. He employed as many as 18 farmhands, who admired and respected him for his fair treatment and good wages. Two elder daughters, Eveanna and Beverly, had moved out and started their adult lives; Nancy, 16, and Kenyon, 15, were in high school. Clutter's wife Bonnie had reportedly been incapacitated by clinical depression and physical ailments since the births of her children, although this was later disputed.
Two ex-convicts recently paroled from the Kansas State Penitentiary, Richard Eugene "Dick" Hickock and Perry Edward Smith, committed the robbery and murders in the early morning hours of November 15, 1959. A former cellmate of Hickock's, Floyd Wells, had worked for Herb Clutter and told Hickock that Clutter kept large amounts of cash in a safe. Hickock soon hatched the idea to steal the safe and start a new life in Mexico. According to Capote, Hickock described his plan as "a cinch, the perfect score." Hickock later contacted Smith, another former cellmate, about committing the robbery with him. In fact, Herb Clutter had no safe and did all his business by check.
After driving more than four hundred miles across the state of Kansas on the evening of November 14, Hickock and Smith arrived in Holcomb, located the Clutter home, and entered through an unlocked door while the family slept. Upon rousing the Clutters and discovering there was no safe, they bound and gagged the family and continued to search for money, but found little else of value in the house. Still determined to leave no witnesses, the pair briefly debated what to do; Smith, notoriously unstable and prone to violent acts in fits of rage, slit Herb Clutter's throat and then shot him in the head. Capote writes that Smith recounted later, "I didn't want to harm the man. I thought he was a very nice gentleman. Soft spoken. I thought so right up to the moment I cut his throat." Kenyon, Nancy, and then Mrs. Clutter were also murdered, each by a single shotgun blast to the head. Hickock and Smith left the crime scene with a small portable radio, a pair of binoculars, and less than fifty dollars in cash.
Smith later claimed in his oral confession that Hickock murdered the two women. When asked to sign his confession, however, Smith refused. According to Capote, he wanted to accept responsibility for all four killings because, he said, he was "sorry for Dick's mother." Smith added, "She's a real sweet person." Hickock always maintained that Smith committed all four killings.