On 8 October 1977, as he did every Saturday, the president of the Provincial Government of Vizcaya, Augusto Unceta Barrenechea went to the Jai Alai pelota court in Guernica —the town where he had previously been mayor— accompanied by his two bodyguards, civil guards Antonio Hernández Fernández Segura and Ángel Rivera Navarrón. They parked in a nearby car park and when Augusto opened the boot of the car to take out his sports bag, he was hit in the head by a gunshot which was followed by a burst of machine-gun fire. Altogether, he was hit eleven times and killed instantly.
His bodyguards reversed the car to try to get away but collided with another car occupied by three people. Antonio Rivera and Antonio Hernández were fired on by the terrorists from a Seat 1430 they had used to travel to the ball court. Ángel Antonio Rivera was shot seventeen times.