Symbolism, Imagery, Allegory
Finding no safe in the Clutter house, Perry and Dick go rummaging through the home looking for whatever cash they can find.
"I [Perry] frisked the girl's room, and I found a little purse, like a doll's purse. Inside it was a silver dollar. I dropped it somehow, and it rolled across the floor. Rolled under a chair. I had to get down on my knees. And then it was like I was outside myself. Watching myself in some nutty movie. It made me sick. […] here I am crawling on my belly to steal a child's silver dollar. One dollar. And I'm crawling on my belly to get it." (3.464)
Perry is thinking about that silver dollar right before he kills Herb:
I knelt down beside Mr. Clutter and the pain of kneeling—I thought of that goddam dollar. Silver dollar. The shame. Disgust [. . .] But I didn't realize what I'd done until I heard the sound. Like somebody drowning. (3.477)
The image of this ruthless killer crawling under a desk to retrieve a young girl's silver dollar is pathetic. The silver dollar symbolizes everything that is absolutely senseless about this crime.