How can Truman Capote be compared to Perry Edward Smith in the book In Cold Blood?

There are a few similarities between Truman Capote and Perry Smith. They were both children of divorced parents. Capote spoke with an odd, childlike voice. Smith was said to still suck his thumb and wet the bed into adulthood. Capote described himself in a letter to Smith as spending much of his childhood "wandering around the South" with his father. Smith idolized his father and followed him wherever he went. Smith's mother was an alcoholic who died while he was a child. Capote's mother committed suicide during his childhood.

Capote himself noted that he and Perry Smith were like brothers: "Truman says it's as if they both grew up in the same household, except Perry went out the back door and Capote went out the front door."