Check that Aznar did not need to "engineer" any attack because he was winning in the polls. The
mastermind behind 3/11, who is still unknown, was clearly someone that did not want Aznar's party to continue ruling Spain.
Check also that before last 2004 National Elections, there was also a
disinformation campaign in order to build up tension in the Spanish public opinion on an imminent ETA big attack.
Therefore, structures that support the Spanish Socialist Party and ETA have collaborated before in manipulating the public opinion.
Probably now they are thinking in something similar. A big terrorist attack is unlikely, however, they may try to stage big impact news, such as rapid conclusion of the negotiations they are carrying out secretly with ETA followed with the surrendering of some weapons; a big operation against ETA in the negotiations aren't sucessful, or even some statements by one of their puppets in the army.
The strategy is to keep the people under tension, so they cannot think rationally. It is like heating a metal, once warm enough you can hit it with a hammer (impacting news) and give it the shape you like. Since they and they collaborators and supporters really control all the media, they can proceed with such tactics.
Check for instance that they are hiding, before an astonished world, the difficult situation of a part of the Spanish
banking sector.
They can fabricate the situation they need. They can even transform an attack
that wasn't Islamist into an Islamist one.
Spain is the perfect dictatorship. And I don't think Rajoy's PP could change that.