Mike Tyson was one of the hardest hitting heavyweight boxers of all time. He was knocking out proven heavyweight contenders (much larger and stronger than the average man) with ease. Many of his knock outs came in the first round. This is evidence enough that he could definitely kill someone with a single punch. If the death wasn't imminent from the punch alone, the victim could subsequently hit their head on a hard concrete which could then kill them. This is the most common cause of a one punch kill. However, despite his age, I believe a Tyson hook would still rip an average man's head off.
Mike Tyson is a very strong man. If his target were not expecting an attack, and were elderly, very small, frail, sick, or otherwise not in full health, a single well-timed, powerful blow could snap a neck, cause internal bleeding, or dislodge a blood clot. Death could be the result of any of these.
I doubt that Mike Tyson could kill with one punch in the present day, but in his prime I don't think it would have presented no problem. I guess we could also ask, "Whe exactly could Mike Tyson kill with one punch?" I don't think he could have killed a heavyweight, but definitely someone of average build and stature.
I think that Mike Tyson has the ability to kill somebody with one punch. While the chances for it are usually slim, there is always the possibility that somebody can die if they get punched hard enough. There are even cases where a light punch can cause death in a person.
I believe that any trained boxer could kill with one punch and that includes Mike Tyson, If you hit a person in certain areas of the throat you can instantly kill them and those who have trained in the art of hitting someone can execute this with probably a good percentage of succeeding.