The Basque police force, Erzaintza, has started an investigation into the source of a letter containing a bullet that was addressed to the 'txupinera' or leader of Bilbao's fiestas, Sonia Polo, sister of jailed ETA terrorist Sergio Polo (pictured).
 
The letter has been condemned by members of the city council as 'absolutely despicable' and an 'attack on a person's freedom and safety'.

The letter was addressed to the 'Head of the Fiestas-Aste Nagusia', Bilbao's famous week of fiestas due to start on Saturday.
 
Sonia Polo's appointment as 'txupinera' of the fiestas was widely criticised by a number of political parties, who felt that her high profile at the event could be used for political means and that she was 'not representative of democratic diversity or of the majority of the citizens'.

The source of the letter, that arrived at Bilbao's Town Hall yesterday, with a 9mm bullet and a press cutting of the 'txupinera' inside is now being investigated.