This highlights one of the problems with 'home defense" that is often cited for example in the need to have a gun in the house. Even cops, who are relatively well trained, can panic, and when you are dealing with someone who likely had little or no training on using the gun, or on how to properly defend themselves with it, things like this will happen. In this case, the pane of glass may be relevant IMO, if the person broke the glass that is next to the door lock where they could conceivable open the door, to me if I was on a jury I would think it could be justified. On the other hand, if the pane of glass that was broken could not be used in opening the door, then I would assume the shooter simply panicked (and if the glass was blown out being shot through by the homeowner, I would vote to convict them of manslaughter).
These kind of tragedies happen, and it isn’t that uncommon. Put it this way, cops and law enforcement agents go through training on appropriate use of deadly force, and even they screw up (read about the Amadou Diallo incident in NYC, for example, where inexperienced cops panicked). It isn’t just about feeling threatened, the fact that the person felt threatened doesn’t matter, what matters is if on review the person had a rational reason to feel threatened.
For example, if someone walks on my property, and I shoot and kill that person from inside my house, in most places you would be convicted of manslaughter or other consequences for misapplying use of deadly force. On the other hand, if I am inside my house, someone comes on my property, and I warn them I am armed and that they better leave, and they continue to come towards my house and myself, ignoring the warnings, it would be a lot more likely it would be found to be justified use of force.
The problem with merely “feeling afraid” as justification is that more than a few people have anxiety disorders and other tendencies where they freak out that to someone outside would appear ridiculous, it is why the reasonable man standard is applied in these cases (I was an alternate on a jury on a case that used reasonable man arguments, and they explained the concept in detail, about how to apply it).
I agree that the article cited is really vague, I would need a lot more detail in this case to determine whether the use of force was justified or not, and obviously what the local law was, too. In Texas you would get away with a lot more things, from what I have read, than you would in NJ when it came to a case like this, in NJ I suspect this guy based on what i know of its laws (as a non lawyer) would be charged.