One Punch Killers

In a split second a person can become a killer or be killed. A One Punch Killer is when someone throws a single punch that results in a death, and often when the perpetrator does not intend to kill, but nevertheless, a single punch that has a devastating effect. But how is this dealt by our laws, when an unfortunate and unexpected criminal act is carried out, when the intention was not to kill and possibly the only intention was to have a good old-fashioned street brawl? Would the perpetrator...