The FELN was founded in February 1964 after the Communist Party of Spain (PCE) abandoned the armed struggle under the leadership of Santiago Carrillo, which resulted in the waning of the activity of the Spanish Maquis.

[1] The new group was led by Julio Álvarez del Vayo and other communists who were disappointed by the PCE's shift in policy and who wanted to keep the armed struggle going against Francoist rule.

Álvarez del Vayo was often gently mocked or dismissed in certain exiled Spanish Republican and Communist circles for harboring an optimism that was not founded on the realities on the ground.

The most high-profile Spanish National Liberation Front activist was Andrés Ruiz Márquez, nicknamed Coronel Montenegro,[10] member of an FELN commando and a former lieutenant of the Francoist Army who excelled in skiing.

The trial would draw public attention in its day because the list of crimes imputed to Coronel Montenegro had been blown out of proportion, including being charged with the planting of a series of explosive devices that had gone off in Madrid in September 1963.