Let's not get too carried away on a wave of vigilante-esque self-righteousness here shall we?
I don't imagine that the shop keeper is making high-fives everywhere over what has happened. He has killed someone, and he has to livev with that for ever, even if the law deems his action not to be illegal.
And before anyone leaps in and says things like "If it was your shop / home ... , 'What would you do ...?' 'They are scum who deserve it ...' and all that nonsense, just think about it.
No-one deserves to die a violent death like this, just as no law-abiding citizen deserves to be burgled, but that does not mean we can all smile and feel vengeful about this terrible incident, and tell ourselves that we'd have done the same.
It's never that simple, and to think that it is is to demean our humanity. So cool the righteous anger, and think about the consequences for all involved.
Ok - right, now you can start ...