How does Harper Lee create a sense of mystery about Boo Radley?

The exposition of the story paints the Radley house as haunted or, at the very least, a scary derelict place. The children talk about ridiculous rumors regarding Boo. Consider Scout's description:

"Boo was about six-and-a-half feet tall, judging from his tracks; he dined on raw squirrels and any cats he could catch, that's why his hands were bloodstained -- if you ate an animal raw, you could never wash the blood off. There was a long jagged scar that ran across his face; what teeth he had were yellow and rottenl his eyes popped, and he drooled most of the time."

Boo, being a mystery, causes all kinds of childish conjecture and fear.