A lot of people dies from just a single punch. He may have beat him for half an hour or he may have landed a strong punch, hard to know for sure.
Even then, even he is not actively attacking someone, you never know if he is going to pull up a knife or something, I wouldn't stop until he is completely harmless as well.
not hard for the coroner to determine that
Yeah, but I was talking more about what little information we have about the situation. I just mean that killing a guy by beating does not automatically mean he kicked his ass for hours.