It was probably not the robbers but the terrorist who are responsible to this. This is one shot and two hits, they have well planned everything and instead of just doing terrorism they also conducted robbery. If they will only conduct terrorism they will lost some people and spent a huge amount of resources in order to be successful, but if they will include robbery they will not only caused terror but also replenished their resources.
Wait, Paraguay have terrorists?! Never heard of that before. I thought it was the more northern countries that have terrorism problems from rebels and drug syndicates.