The background
The book played a big part in the text used on the front cover - ‘thou shalt not kill’ because the town was mainly Christian, it is the sixth commandment and is repeated six times because of the 6 people who died, linking it all together. But the mean overall look of the cover comes from ‘Bastille Four Walls’, which is based on Perry Smith who is a key character in the book.
See more about the design on my website here