50 years ago this spring, Perry Smith and Dick Hickock were hanged by their necks until they were dead. The crime that earned the death penalty for both men has since become one of the most infamous in American history: the 1959 quadruple murder of an innocent Kansas farm family, in pursuit of the contents of a safe that turned out to be nonexistent.

The tale of that six-year period between 1959 and 1965 was told in Truman Capote’s In Cold Blood, an explosive bestseller that disappointed its author only because it failed to earn a Pulitzer. Capote’s book catalyzed the “nonfiction novel” genre, which now yields many of publishing’s most popular books each year.

Few authors, though, have written anything that compares in elegance and power to Capote’s masterpiece. Based on thousands of pages of notes amassed by Capote and his friend Harper Lee, who aided in the investigation, the book is inspired and haunting. What gives the book the feel of a novel, as much as the lucid prose and invented scenes, is its structure: first we meet the victims, then we follow the crime’s aftermath. Only near the book’s end do we learn precisely what happened in the Clutter family’s house that terrible night.

There have been persistent rumors that Lee actually wrote In Cold Blood; that’s a greatly exaggerated version of the truth, which is that Lee worked closely with Capote on the research and development of the book, and was hurt when Capote publicly characterized her contributions as only “secretarial help.” For the past half-century, as the world has waited for what it thought would never come—a second novel by Lee, now being published this summer—In Cold Blood has stood as a dark companion volume to Lee’s iconic 1960 novel To Kill a Mockingbird.

Lee’s book was also inspired by true events, though much more loosely. It’s told from the perspective of a child, and the question it asks is wrenchingly elemental: how are we to live with the knowledge that the world is unfair? Atticus Finch has become one of the quintessential literary archetypes of parenthood; of the adult who must communicate to a child that there is love in the world, even if there is also hate.

A biographer of Lee, Charles J. Shields, has indicated that Lee was disappointed Capote didn’t make the murder victims more complex; indeed, in To Kill a Mockingbird it’s the sympathetic characters who are complicated, while the villains are relatively simple. There’s a nod to the idea that the Ewell family has been hurt by poverty and addiction, but vile paterfamilias Bob Ewell is also clearly painted as the chief architect of his own family’s suffering.

In Cold Blood, by contrast, is absolutely fascinated by its villains. The murder case provides a plot, but the core of the book is its detailed personal histories of Smith and Hickock. Though Capote never apologizes for them—and the question of their own regret, or lack thereof, is ambiguous—he tells us more and more and more about each man, particularly Smith, until we feel we understand why so many murders are also suicides.

The book is a study in self-loathing, and in the complexities of mental illness. Hickock’s antisocial tendencies may have been exacerbated by a head injury, and Smith grew up in a savagely abusive environment, but ultimately both men were judged to bear responsibility for their actions. Capote doesn’t try to absolve them, but he does demonstrate how starkly limited the men’s horizons were—or, at least, how limited Smith and Hickock understood them to be.

Both In Cold Blood and To Kill a Mockingbird unfold in small-town settings, and both remain so compelling because they cast light on one of life’s most difficult truths. Some writers regard small-town life as a haven of human kindness and gentle foibles, while others see it as a theater of petty jealousies and casual cruelties (see, for example, Garrison Keillor and J.K. Rowling respectively), but Lee and Capote ask a troubling question: what if people are essentially good, and also capable of vicious violence to one another? It’s that irreducible also that haunts our lives, and our literature.

– Jay Gabler