5 year old on a rampage.....

Okay, I hope I can get some help from friends, family, and at this point total strangers. My 5 year old nephew has fell completely off the deep end. He has always been the sweetest, most loving boy you have ever met, getting a citizenship award at school, and the teacher saying how he was the most caring child she'd ever had. In a matter of months he has become mean, hateful, and having terrible fits of rage over nothing. It takes very little to set him off. He has been to the principals office twice in a week and has threatened to "punch in the face," several loved ones. We have tried punishment, rewards, and begging! Nothing has worked. I am "Love & Logic" trained and have never seen a child that it didn't work on, until now. We have talked to him in length about what is causing this anger, nothing. We have now taken him out of daycare before and after school and he is going to my house. Any suggestions?