JDR-Probably for the same reasons about 95% of drive-by shootings are never resolved in L.A.: the criminals blend in too easily to their surroundings upon completion of their "acts". Masked hooligans remove their masks, and "voilá" no longer are they the "guy in the mask who did such-and-such". They're now just another "innocent" bystander. For a detailed explanation of why no arrests are made, I suggest a call to the local Ertzaina station.
I reiterate, that these are not "a sueldo" (paid by ETA) yet, but are just kids who would like to be, but aren't yet. That explains their willingness, Fernando. I also reiterate that when confronted, most of them would wet themselves, rat out their friends, and cry for mommy like any other frightened wuss who hides behind a mask.
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Ongi etorri!