Like the concerned woman who reported him to the police?
The proper thing to do - as said in the article - is for the police to investigate if he was serious. And you or I would - depending on lots of context on whether we thought it a remotely credible threat I guess - report it for them to investigate?
The problem seems to be on the police end, not the concerned citizen (of another country) end.
No. Not at all. Have you not read what is commonly spouted on the internet? You have to be 100% illiterate to not understand that this was tasteless sarcasm.
This doesn't mean I think it is funny or that I agree with it, but calling the police over a joke is pointless and irresponsible.
However, this is like putting out a candle with a fire hose.
The inability to discern the difference hints at mental issues that need to be discussed with someone, even a parent would do.
To me, it looks like the inability to discern the differences is not with Justin.
However, I do believe that if you say "I'm going to murder children" in a public forum in a country where that exact thing happened on a disgusting level recently... you should get some counseling.
Every teen has at one occasion thought: I feel like killing [everyone in school, my team, my so-called friends, my brother, my ...]. Writing such a thought down gives it extra power and a screen doesn't confront you with a person and make it easy to misjudge whether you can press 'send'.
Monitoring that speech and acting on it, directly by the government or indirectly via 'concerned citizens': that way lies police state insanity.
So the answer is emphatically, decisively: no. You should not want to report this.
By these standards, you'd have to arrest every teenager in America eventually. That isn't an exaggeration.