Although I have never killed anyone, I am convinced that a good punch to the throath is fatal if the injury is not treated quickly.
When sparring, I have received punches to the nose, jaw, temple, ribs, and kicks to the knee, stomach and groin. All of those hurt but none of those ever put me out of commission. But once, I received a very light strike to the throath (an accidental strike that was not even intended to hit me!), and I could not breathe for a few seconds or swallow my own saliva for a few minutes or eat properly for the rest of the day. Imagine if it had been a real punch. I would have ended up in the operation room.
The wind-pipe is a very delicate part of the anatomy. I have heard that one of the "ancestors" of my kung fu style once ended a fight to the death with a first strike to the throath.
I tell you all: hit someone with a "phoenix eye" punch to the throath and your opponent is as good as dead. So be responsible and go for the throath in life and death situations only!