Arthur "Boo" Radley's troubles began when he was a teenager and began running around with the "wrong crowd"--the Cunninghams from Old Sarum. He was arrested for disturbing the peace, disorderly conduct, assault and battery and "using abusive and profane language in the presence and hearing of a female." The charges were somewhat exaggerated, since the group's actions were little more than a boyish prank, but the whole group was sentenced to the state industrial school. Arthur's father would not allow young Boo to go, and he convinced the judge to release Boo into his custody. Boo was confined to the Radley house and "Mr. Radley's boy was not seen again for 15 years.
Boo apparently had no say in the matter, and he must have deteriorated--mentally and physically--greatly during his lengthy home confinement. When he was next heard from again, it was because he had stabbed his father with a pair of scissors. This time, Boo was locked in the basement of the courthouse--"The sheriff hadn't the heart to put him in jail alongside Negroes"--until his father took Boo back home again.
Nearly all of the rumors about Boo had no basis in fact and no witnesses to support them. His purported peeping in windows at night, slaughtering pets and animals, and poisoning pecans were all unfounded. Instead, Jem and Scout discovered that he was a man in need of young friends, even if he wasn't willing to leave his house to meet them. Jem and Scout eventually recognized that the gifts in the secret knothole of the Radley oak were from Boo, and that he meant no harm. The children decided to respect his privacy, and they hounded him no more.
No one knew just how closely Boo watched the Finch children, but he was there when they needed him on the night of the Halloween pageant. After he saved their lives, killing Bob Ewell in the process, Scout understood that he was a neighbor who had not received acts of kindness in return. Scout recognized Boo's plight and his true feelings when she stood on his porch in the final chapter, gazing upon the neighborhood and seeing the events of the past two years through Boo's eyes. What he must have seen was not much different from what Scout remembered--summetime, children playing, colorful azaleas, a burning house, a shot dog.
Atticus was right. One time he said you really never knew a person until you stand in his shoes and walk around in them. Just standing on the Radley porch was enough.