As time went by, Jem came to realize that Boo Radley was not the terrible "boogie man" that he and Scout (and Dill) had imagined. It began on the night that Jem lost his pants, when he returned to find the tears sewn "all crooked." He told Scout that it was "Like somebody was reading my mind." Later, after discovering the pocket watch and chain along with the knife, he told his sister that "I just don't get it... I don't know why, Scout." Then, on the night of the fire when Atticus informed them that it must have been Boo who had quietly placed the blanket around Scout, Jem told her that "I ain't gonna do anything to him."
In Chapter 23, after discussing the Cunninghams, Atticus tells the children that "there's just one kind of folks. Folks." Jem thinks for a moment and then tells Scout that he thinks he understands why Boo stays inside his house: "... it's because he wants to stay inside."
When they were younger the kids believed that Boo Radley was a myth and in fact made up many stories in order to figure out why he was isolated. Yet as the kids grew older and Jem started to have more values of his father instilled in him, he realized that Boo is just a person and he did nothing wrong.
In the book "To Kill a Mockingbird" Jem describes Boo Radley to Dill and Scout. He tells them that at night he has seen Boo's tracks in their backyard. He describes Boo Radley as being over six and a half feet in height. He is basing this on the size of his tracks not from seeing him. He says he eats raw squirrels and if can catch them, he also eats cats. His hands are always stained with blood. He had a long scar running down the side of his face that is jagged. His teeth are yellow in color and look rotten. His eyes are pop-eyed and he drools all of the time. In essence, Jem has made Boo sound like the perfect boogie man.(Page 13)