Since you seem to be new to the whole self defense thing I'll try to answer your question.
You may shoot someone in self defense only if they present,or appear to present, a direct threat to you or someone else at the mment you pull the trigger. Period. Thats it. No other time.
If he is pointing a gun at you or a family member, or is in the act of doing so, you may fire to defend yourself. If he turns away and walks off, regardles of what else he did before that, then you may NOT legally shoot.
Dude breaks in, hold you at gun point, beats you and the kids, rapes your wife, and steals your mothers ashes from the urn on the mantle and leaves. As he walks away down the street you retrieve your gun and shoot him in the back.
Thats murder. Period.
The threat had passed. Now, same dude is walking away and turns around to come back, maybe for a little something more? Now he's a threat. Now you can shoot.
Bottom line. They must be a direct threat at the time of engagement or yu can't shoot.