Yelling a warning is what the cops do. I'm not a cop. This guy did the right thing all the way. Why should someone breaking into your home be given a chance?? If that guy had been armed and the owner yelled a warning the criminal might have started shooting into the house where the owners family was at.
Nope, no warning needed. Only thing needed in a situation like that is propper sight alignement, good breathing, and a steady squeeze on the trigger, no more bad guy, problem solved for good.