Op, what medication is he taking for depression? From your description, it doesn't sound like the depression medication is doing what it is suppose to do. I would talk to his psychiatrist about your concerns. Maybe your DS's behavior is normal or maybe his medication should be adjusted. It also sounds like your DS would really benefit from therapy. Someone outside the family that he can talk to about his frustrations would be very helpful, I think. The therapist could really help you understand what tactic you should take with him too.
" I object to violence because when it appears to do good, the good is only temporary; the evil it does is permanent." Mahatma Gandhi
"This is the ultimate weakness of violence: It multiplies evil and violence in the universe. It doesn't solve any problems." Martin Luther King, Jr.