Car bomb explodes in northern Spanish city of Madrid . Basque president : kills a national police officer named Eduardo Puelles . Spain : It was caused by a limpet bomb placed underneath the car . Events in Basque country at heart of long - running separatist conflict .
Car bomb explodes in northern Spanish city of Arrigorriaga . Basque president : Victim a national police officer named Eduardo Puelles . Official : Explosion was caused by a limpet bomb placed underneath the car . Arrogorriaga in Basque region at heart of long-running separatist campaign .