My concealed carry instructor taught these 4 precursors to using deadly force:
1. Intent - Does the perp have intent to cause you or others harm?
2. Ability - Does the per have the physical ability to harm you or others?
3. Opportunity - Does the perp have the spacial ability (no barriers between you and them)?
4. Jeopardy - Does the perp give you no other opportunity to exit the situation?
Obviously you can't go through this list while in a highly intense situation.
However, these should be common sense and you should be able to go through them in a split second.
Because he was outside, breaking in, and the home owner couldn't see him, 1,2 and 3 were not obtainable.
If it were I in the same situation, I would have notified the person that I had a gun.
At least my conscience would be at ease after I took his life.
I am not of the shoot now, ask questions later bunch.