They simply could set off a loud explosion at the end of a concert as people are leaving to cause mass panic. People obviously think a bomb has gone off and Herd Mentality takes over with people running and screaming. Of course this is what's shown all over the media, we will never see the actual Bomb Explosion because there was no bomb.
Moreover, the firefighters tried to help but they were stopped from doing so...probably for not ending and exposing the circus? maybe because after all they could not rescue anyone because no one was dead or injured? http://www.mirror.co.uk/news/uk-news/firefighters-angry-were-stopped-helping-10492990
I am not an expert in this issues, but I definitely can see something fishy is going on here.
But a truther, named Ole Dammergard who researches this for years might explain you better than me, he concluded that a lot of the supposed terror attacks happenning in Europe and USA were staged with the precious help of crisis actors helping and media liers...and this "company" might be one behind this events http://www.crisis-solutions.com/
take a listen to his interview.
There are tons of truthers on the internet that research of false flags and staged hoaxes, if you prefer a shorter video I think this one is very good:
TV sells us fiction all the time (soap operas, reality shows, movies...)...it is not surprising that they keep making fiction out of reality in the news...TV can't tell you the reality, news sell you an opinion made to program you, they foccus on bad things to keep you in a state of fear and therefore controlled, the news are picked by whom? why are they always bad? who decides which events are worth and coverage and which are not? how can you be sure the news are not made up? why do you trust the news?It is very sad to see lots of people treat me like a mentally ill retarded just to make questions or to doubt the narrative of the main stream media, but I understand they were indocrinated by the system and they are reacting because they can't stand the fact they have been lied to all their lives....it is easier to fool someone than convincing them they have been fooled!
Don't be fooled!