In chapter 1, we know that Radly's house was viewed as a haunted house where there lives a ghost called Boo radly, the people say that he kills living creatures, and mutilate them.
But soon we know that boo is a 33 yeared old man, that was mistreated by his father. One day he stabbed his father on his foot, He was then sent to the jail, but was at last sent back to the Radly's place, and when his father died, his older brother moved back and stayed with him.