If he were breaking into your home while you were in it, then yes you can use deadly force to defend yourself. If he broke into someone else's home and nobody's life was at risk, call the police and let them take care of this.

If you want to put yourself at risk (legal and or physical) by engaging as a 3rd party, be prepared to suffer the consequences. If you bring a firearm into the situation, understand that you have now raised the stakes and it might cost you your livelihood or your life.

These guys should have simply called the police and kept their distance until the police arrived. Now they have to deal with the consequences of being ignorant.