do juvenile boot camp changes teenagers?

20 years ago my brother committed a criminal offense and he was sentence 6 months into a boot camp when he was 16 years old. before he was sent to boot camp, he was very friendly, very kind. he never picked a fight in his life. his mistake was that he stabbed another student at school with a pen as self defense but nobody bought it. he was charged with assault with a deadly weapon. the person he stabbed was a bully he always picked on my brother until my brother was fed up and attack back with a pen. when he was released from boot camp he was a different person. he was strong, he was not sensitive, he wasn't afraid to pick a fight anymore, he learned how to fight, he stopped going to church, he wasn't weak or sad anymore, he is always mad, he became an atheist, he didn't care about other people's feelings. he became a cold hearted person and cruel person and if anyone messes with him he will beat that person without thinking it. what do they do to teenagers at boot camps? i don't feel confortable to ask my brother, but does anyone know what do they do to teens in boot camps? do they change them like they change my brother?