What do we know for certain about Boo Radley in To Kill a Mockingbird?
Needless to say, most of the information Jem and Scout receive about their unseen neighbor Boo Radley--that he "peeped in windows," froze azaleas with his breath, mutilated animals and poisoned pecans--is merely speculative gossip spread by the "neighborhood scold," Miss Stephanie Crawford. We do know that Boo was arrested with some of the Cunningham boys from Old Sarum and
... came before the probate judge on charges of disorderly conduct, disturbing the peace, assault and battery, and using abusive and profane language in the presence and hearing of a female. (Chapter 1)
Arthur Radley Jr. was released into the custody of his father,
... and Mr. Radley's boy was not seen again for fifteen years. (Chapter 1)
Boo was next seen again after he apparently stabbed his father in the leg with a pair of scissors, but old Mr. Radley "insisted that Boo not be charged with anything." Since
The sheriff hadn't the heart to put him in jail alongside Negroes... Boo was locked in the courthouse basement. (Chapter 1)
Though Scout wonders if Boo is still alive, she is assured that he is since no one had seen his body carried out. Miss Maudie tells Scout that she remembers Boo speaking "nicely to me, no matter what folks said he did. Spoke as nicely as he knew how."
Most everything else about Boo is strictly speculative in Part One, including whether it was Boo that Scout heard laughing after she crashed on the Radleys' front steps; whether it was actually Boo's shadow the children saw on the Radleys' back porch; or whether it was Boo who placed the blanket upon Scout's shoulders on the night of Miss Maudie's house fire. In all three cases, it was probably Boo, but as always, the "malevolent phantom" was never seen.