It won't necessarily be clear what could have caused the explosion for some time. The police urging caution under those circumstances is not surprising. This sort of speculation ought to be a bannable offense and I wish the NeoGAF moderators would take it more seriously.
https://mobile.twitter.com/NBCNightlyNews/status/866806307159986176
I mean, it wasn't as if I speculated something so out of the ordinary, that a massive explosion at a public place with tons of individuals in the 21st century, wouldn't possibly be some sort of domestic/foreign attack. There is a reason we go to believing it is an attack because almost always that is what it is. But keep backseat moderating I guess.
Rest in peace for the victims. This hits hard because you think of little kids going to see their favorite pop stars and are innocent.