There's nothing "awesome" about something like this which is a fucking tragedy to begin with.
In my opinion one should really consider the bigger implications of devaluing human life before deciding on (what is once again in my opinion) such a crude definition of justice as this.
The cop did his job, but a hero? Not really.
I'm troubled here. I don't know whether I find your teenage naïvety cute or outright obnoxious. Typical Swedish left wing wannabe kid who claims injustice for the sake of voicing his opinion.
A worthless and harmful individual was removed from existence, there is absolutely nothing tragic about that. You may think so, living in luxury in your little bubble that is social welfare and security - but for the people that live in high crime rate areas, people like him are a plague. Do you think that was his first offense? That he was suddenly struck with an epiphany one day?
"Gee williker! I normally don't carry guns on me, but I've been wanting that flat screen TV for a while. Better go rob some poor fucker, fuck living an honest life!"
He was most likely already an unlawful citizen, only this time, retribution was close at hand.
You'll probably argue that he is not the root of the evil and therefore should be treated humanely, and you'd argue partly correct.
He is not the root of the issue, that I concede. Because, why would he? He's just some idiot with an already bleak outlook on life. If he didn't get killed by that cop, he'd probably still be dead within no more than 10 years unless he was lucky. The root of evil is many things and I doubt I could list them all without challenging your attention span, but the main issue here still isn't that the guy was given no consideration to his life, but that individuals like him are not discouraged enough to live a life of crime.
The off-duty police officer acted with quick and just judgment, I'm fairly positive that the majority of his fellow policemen agreed with the decision. Not only his peers but other people that are daily subjected to armed robbery, violence and similar vile acts would also feel inclined to be comforted by his deed.
A cancerous rat like him should be dealt with no mercy. At least until the cure for that cancer is discovered, but that will most likely not be within our lifetime. Until then, guys like him deserve no sympathy, for others may follow in his crime ridden endeavours.