What hints suggest that Boo is not the "monster" he is made out to be in To Kill a Mockingbird?
First, the crimes of which Boo is blamed are mostly ridiculous and unsubstantiated: Though he was accused of mutilating animals, the culprit was actually Crazy Addie; no one ever died from the "poisoned" pecans from the Radley tree; and even Boo cannot be blamed for frozen azaleas. The unexplained items found in the knothole of the Radley oak tree were the first hints that Boo was more kindly than monstrous. But perhaps the most obvious clue was when Scout noticed an unusual response after Atticus had caught the children playing their Radley Game.
Through all the head-shaking, quelling of nausea, and Jem-yelling, I had heard another sound, so low it could not have come from the sidewalk. Someone inside the house was laughing.
Of course it could have been Boo's brother, Nathan, that Scout heard laughing, but the possibility became clear that it could have come from Boo. The children get another shock during their raid on the Radley's back porch when Jem encounters a shadow.
The shadow stopped about a foot beyond Jem. Its arm came out from its side, dropped and was still. Then it turned and moved back across Jem, walked along the porch, and off the side of the house, returning as it had come.
Again, the shadow could have been Nathan's, and Boo's brother could also have mended the pants that Jem found later that night "folded across the fence." But Nathan had cemented the knothole and had fired a shotgun blast to scare the children, so Boo was the most likely candidate. When the blanket mysteriously appeared on Scout's shoulders on the night of Miss Maudie's house fire (while Nathan was "tuggin' that mattress"), it became clear to Atticus that only Boo could have placed it there. When he announced this to his children, they both suddenly understood that Boo was no one to be feared.