By Robert Graysmith. A classic in the genre, rather melodramatically written, but then that's not unusual. Graysmith's books on the case descend into some crackpottery but this first one is a foundation text.
It's somewhat rare to come across a secondhand PB edition in readable shape; seems people hold onto their copies until they fall apart. This one is fairly well-kept: some edgewear, page toning, and a cracked spine that's faintly faded, but no tears; one or two tiny dog-ears; and it sits very straight. A great reading copy.