While the 1967 film of the same title that stars Robert Blake as Perry Smith faithfully chronicles the journalistic fiction of Truman Capote, who was very involved in the making of this movie, there is no substitute for having read the book which provides insights into characters and much more detail. However, since the limitation of time is a factor, reading the study guides on themes, character analysis, as well as the summary will certainly help.
Capote's book is divided into four parts, which are extensively detailed:
- The character of the Clutter family, their social status and activities during the last day prior to the murders
- The planning and plotting of the killers
- The detailed investigations of the Kansas Bureau of Investigation (KBI) agents
- The capture, trial, and execution of the murderers.
So, you may wish to examine each section, especially part II in which a psychological study is made of Perry by Capote, who explores the theme of "Nature vs Nurture." Capote become sympathetic to Perry Smith, whose history is one of physical abuse and neglect and, thus, raises the question if Smith should be held completely responsible for his actions when he is a product of his environment.
P.S. There is really never any substitute for having read the main literary work.