Sister In-Laws Son Killed My Kitten

My sister in-law's son is 7 years old.  Supposively she said he has ADHD.  She sometimes takes him to a psychiatrist but hasn't in a long time.  He doesn't listen to anyone.  Every time we tell him he's doing wrong or punish him he'll listen for a couple minutes than goes off and acts up again.  He's great at school with it comes to learning but he's always punching kids and being very aggressive.  On November 1st he killed one of my kittens when my fiance and I were gone.  (The kittens stay at our parents house, so does the nephew and sister in-law)  When we asked him what he did he kept changing his story or would leave out details about what he did.  Than we found the dead kitten with the mother and he told us that he kicked it off the porch and dropped a large rock on it.  We asked why he would do such a thing and he said because he wanted to and because it was the 1st of November.  We are really tired of this and don't understand.  Does he need to go see a doctor alot more than he has been?  Everyone is tired and it just seems like his mother isn't doing what she should be.  I heard children who kill or torture animals lead to having a criminal life.

[Roger Gould, M.D.]

You are describing a very, very serious problem...can and probably will get worse without treatment..yes, he must see a  psychiatrist, and quite intensively, this is not something he will just grow out of...