It's not about whether the other guy is armed or not. While I can't speak for other jurisdictions, in the UK it's about what's reasonable in the circumstances (

It's not about whether the other guy is armed or not. While I can't speak for other jurisdictions, in the UK it's about what's reasonable in the circumstances (with allowance made for the fact that someone in that situation does not have the time to make a full objective assessment of the situation). Sure, if the person attacking me is unarmed and I'm bigger, stronger, wearing armour and carrying a baton, shooting them might be considered unreasonable (but might be considered reasonable). If I'm in fear of my life and all I have is a handgun, shooting them is very reasonable. Of course, in the UK, the next question from the police would be "What's with the handgun?" :) All that said, in the case of Alan Pean in the article, I could well believe that the two off-duty police officers moonlighting as security guards were basically incompetent amateurs with weaponry, believing their own hype.