In Truman Capote's jounalistic novel, In Cold Blood, he reports on the horrific crime of the murder of the Clutter family while examining closely the men who committed this crime. Capote particularly found Perry Smith fascinating. His visits and conversations with Perry led Capote to raise the question of whether a man alone can be held responsible for his actions when his environment has deprived him of what is essential to a human being. This exploration into the psyche of Perry Smith develops the theme of Nature vs. Nurture. Were Perry's crimes the acts of one who was inherently evil, or did they stem from his neglect?
Another theme in Capote's book is that of Sexuality. Hickock who cannot be satisfied with monogamy has been married twice. But, he is also perverted as Smith has to prevent him from raping Nancy Clutter on the fateful night. Smith, who complains that he cannot stand people who do not control their sexual urges, seems to struggle against his homosexuality. He constantly tries to prove his masculinity to Hickock, who, in turn, strives to prove his potential to violence to Smith.
It seems to me that the two main themes of In Cold Blood are the very old and traditional theme of crime and punishment and the more modern theme that nobody is safe anymore in our modern world. As far as the second theme is concerned, the Clutter family would have been safe in older times because they lived in such a small and isolated community. But with automobiles and superhighways we see a pair of desperados drive all the way across the state of Kansas to intrude into the lives of innocent strangers and then all the way back. There is also the incident in which the two murderers plan to hitchhike and murder the driver so that they can steal his car. No one is safe anymore. We see virtually no hitchhikers anymore because everyone is afraid to pick them up, and for good reason.