Definitely tragic.
Imo, any intruder is life threatening, but he should have ID'd his target.
It depends on the jurisdiction. In some states you could indeed shoot someone attempting to enter your residence as you have a legal right to assume they are doing so with the intent of committing murder, rape or great bodily harm to you or your family. In other states you cannot.
Once inside your house the rules may change depending on the jurisdiction. For example in some states I could legally assume that if you are in my house you are there to commit murder, rape, etc, and again legitimately use lethal force. In other states I may have a burden to retreat and in yet other states my options might depend on what you are doing. If you are advancing on me with a weapon that's probably sufficient justification in many of not most jurisdictions. However if you are just trying to run out the back door with my TV in many of not most jurisdictions anything more than physical force is probably excessive.
VA is a good example, where you can shoot someone breaking in the front door, but not running out the back door. Even in the first case, VA is an affirmative defense state and you'd have to be arrested and charged with second degree murder and then demonstrate in court that You had a legitimate justification of self defense for the homicide. Plan on big bucks and lots of stress, job loss, etc, unless it is an absolutely, ridiculously clear case of self defense where the prosecutor would be looking like an idiot charging you and prosecuting you.
Then there are little oddities and distinctions. In NC for example, you can shoot someone who broke into your attached garage, but if it's an unattached garage, it's just a properly crime and you cannot employ lethal force.
The short story here is know your local laws pertaining to lethal force as well as those in any state you might be concealed carrying in as you travel.
Also keep in mind that you are legally speaking always better off if you have not just a legal justification to shoot, but also a very compelling *need* to shoot in the form of a *total lack* of other options.