He has a brain problem - this can happen to dogs - it's called Rage. The dog has no idea what it is doing, but unfortunately every case I've ever heard of the dog had to be put down. There is no cure and the dog could kill someone.
Very sad. Sorry
Even vets who don't think rage is the case will tell you this:
When treating any dominant aggressive dog, the prognosis depends on several factors:
1. Age of onset of aggression – The younger the dog at the time of the initial aggression, the poorer the prognosis. Most dominance aggression begins around the age of behavioral maturity, 1-2 years of age. I have seen some dogs that already showed severe signs before 6 months of age. On the other hand, I’ve seen some owners who don’t seek help until the dog is approaching middle age, although the initial warning signs were present much earlier.
2. Duration of aggression – Since there is a learned component in any form of aggressive behavior, it makes sense that the longer the aggression has been going on, the harder it will be to convince the dog the household rules have changed. Like any habit, owner behaviors that lead to aggression are also harder to change.
3. Severity of the aggression – Dogs who display lower levels of aggressive behavior, such as growls, lip curls, and inhibited snaps, will be much easier to treat than dogs who explode with violent attacks. The severity of the displays is a stronger predicting factor for successful treatment than the frequency. There is certainly less owner motivation for attempting treatment when the attacks result in severe injury, even when they are very infrequent.
4. Predictability of the aggression – If owners can predict which situations are most likely to result in aggression, such as guarding objects or a favored resting place, then measures can be taken to prevent those situations. In addition, safe training sessions can be set up to teach alternative behaviors. If an owner, even with the help of an experienced behaviorist, cannot predict the aggression, it will be far more difficult to treat.
Sounds like your dog is a not a good prospect.