The Question and Answer section for In Cold Blood is a great resource to ask questions, find answers, and discuss the novel.
From the text:
The polygraph machine had eliminated Bobby.
Dick's parents thought Perry was trouble.
"Dick brought him [Perry] home one evening, and told us he was a friend just off a bus from Las Vegas, and he wanted to know couldn't he sleep here, stay here awhile," Mrs. Hickock said. "No, sir, I...
Dick and Perry planned to kill the owner who picked them up and take his car. Their plan was foiled when the salesman picked up another hitchhiker.