Arthur Jr. had previously been jailed when he was still a teenager after getting into trouble with some of the Cunningham boys. While the other boys were sent to the state industrial school, Arthur's father got his son released to his own custody. He apparently locked Arthur Jr. away inside the Radley house, and "Mr. Radley's boy was not seen again for fifteen years." It was at this point that Boo, now 33 years old, ran into trouble again. He was led from the Radley house after he had suddenly plunged a pair of scissors into his father's leg. Afterward, Bo
... pulled them out, wiped them on his pants, and resumed his activities. (Chapter 1)
But, "Boo wasn't crazy, he was high strung at times."
... he was not a criminal. The sheriff hadn't the heart to put him in jail alongside Negroes, so Boo was locked in the courthouse basement. (Chapter 1)
Arthur's father soon had him out of the basement and back into Boo's own prison surrounded by the walls of the Radley house.