 This attack was carried out on 20 December 1973.An ETA commando group using the code name Txikia (after the nom de guerre of ETA activist Eustakio Mendizabal killed by the Guardia Civil in April 1973) rented a basement flat at Calle Claudio Coello 104, Madrid on the route over which Carrero Blanco used to go to Mass at San Francisco de Borja church.Over five months, this group dug a tunnel under the street - telling the landlord that they were student sculptors to disguise their real purpose.