How can this happen?

Greece is a bankrupt country with a mass unemployment. It has a massive problems with refugees coming into it. 

With all this going on, who the hell has time to produce a bomb and do this:

http://www.xinhuanet.com/english/2018-12/27/c_137702738.htm

That it has happened would leave you have to wonder what is the basis for such an action and to who is it really addressed to and what is the desired aim for this explosive brouhaha?

Does anyone know?

The interesting thing is I now find that Greece for all her woes and tribulations, is a place of terrorist acts. However, when it comes to explosives, the terrorist groups doing them have always forewarned the Greeks and identified themselves. But not this recent one!