I am not in favor of executions or vigilantism, but if you read between the lines of the story, there are some things in the homeowner's favor.
First, his reason for confronting the trespasser - there was a history of recent thefts in the neighborhood ("burglars have taken all-terrain vehicles, tools, bicycles, and navigation and stereo equipment") and the homeowner had a shop or shed at his home where he stored "construction equipment." It isn't clear whether he is talking about backhoes or circular saws, but he certainly had an interest in protecting the equipment that he used to make a living, and it is understandable that he might exercise that interest by confronting a trespasser and potential thief.
Secondly, as has been brought out by a couple of previous posts, the teen responded to being ordered off the property by an armed homeowner by advancing on the property owner. That would seem to be a clear escalation and threat.
Certainly things could have been done better; most especially he should have called 911 at the beginning rather than at the end of the episode. But I just read another thread in which the police responded to a report of a thief brazenly stealing car parts in the driveway of a man's car with the owner standing there watching by promising to be there in thirty minutes. And I personally recently waited an hour and forty minutes for a response to a car accident after being rear-ended at a railroad crossing.
I know our LE agencies are overworked and undermanned and underfunded, and I don't blame them, but the inevitable result of slow response when people's lives, homes, and livelihoods are threatened are that they will act to protect their interests. If, as a society, we are going to abrogate the government's role in protecting its citizens, we must accept that they will protect themselves. In a certain way, we seem to be going backward to the situation that caused our founding fathers to call for citizens to arm themselves and participate in their own protection.