I wouldn't be surprised if that's the case. When we first met him he seemed like a sweet, shy kid and recently the bully's come out in him so either it's the friends he keeps (other neighborhood bullies) or someone's being a bully to him at home.
One of the biggest bullies in my class one year was the student who was geeky and didn't fit in, and was acutely aware that other children were smarter and more "cool" than he was. You would have thought he was the victim, but he was the instigator. His parents were also getting a divorce.
Bullies fall into several categories. One is, the child is truly a bully, who has been taught that mean equals survival. This is a kid who may feel insecure, but doesn't respond at all to empathy speeches . This is a hard core case that responds only to Bigger Authority stepping in.
Second case, is Insecure Kid just acting out. This kid wants to make others come to his/her level. This kid feels some empathy, but is really kind of clueless (hasn't been taught social clues, so tends to get left out or acts inappropriately) and is using the wrong methods to fit in.
Third case, is just ordinary "mean girl" kind of behavior. This is just the usual playground cliques and normal child bad behavior.
I would never accuse a child of lying, because it simply doesn't work well with them. If they're denying something they did, I use the
"You need to take responsibility for what you did" rather than head off into the emotional words of lying, etc.
The "How's that working for you" is a really powerful line with children, because it asks them to look at how their choices and responses are actually working.
Piratelvr, my suggestions would be to keep to keep it short and simple verbally with this kid.
"You tried to beat them up yesterday, They don't want to play with you today. When you threaten to hit people, they don't want be around you."
"I can see by your face you feel sad about that (labeling his emotions for him, since he's probably had very little help with this) and I can tell you want to do better. So tomorrow, if you are nice to them, we can see about you playing here."
I sadly, and seriously, think the parents will be of little help here. Best to concentrate all energy and efforts on teaching this little boy some basic understandings of relationships