What's wrong wiht my adopted Nephew 2? (i Added more detail to the question)?

my brother adopted his wife's son Shaq. he's been in our life since he was a baby he has no clue he's adopted. We've taken him to all 4 disney parks. We play videos games. go to the park with him we do alot for him. We do the world and then some for this kid. we always give him attention. We treat him like gold.Shaq (my nephew) is bipolar. The kid is 10 years old this kid is bad. I mean my cousin Brian is bipolar and is nothing like this kid. We've given this kid the world and he's still is terrible. He tried to drown my 3 year old cousin Christian in the pool and he was laughing at him when he was doing it. I've caught him punching my brother's dog Winnie. Kicking my cat in the face. He's locked my niece Cherish who's 2 in my parent’s bedroom at night with no light on. He's sprayed mosquito repellent on my cat's kittens, one of the kittens died cause of it. He back talks to my parents. We can't leave any money on our kitchen table when he's around because he steals it. He's played with my knife collection cutting up pages in one of my school books. He didn't want to go back to cl one day so the kid went in the bathroom stalls, the school had a lock down cause they thought the kid was abducted. He has no respect for authority figures. He’s been held back twice. I know he's got something else wrong in his head. Please someone tell me what else could it possibly be? Why does he do this?