During the past 13 years about 6,300 bodies have been exhumed from mass graves of which 2,500 have been identified, according to Emilio Silva, who heads the Association for the Recovery of Historical Memory which spearheads efforts to help people find the remains of relatives who went missing during the Spanish civil war.
"But the criminal justice system did not take action in any of these cases," he said.
Five years ago 36 civic associations filed hundreds of complaints regarding the murder and disappearance of 114,000 people during Spain's civil war, and the early years of the dictatorship that followed, with crusading human rights judge Baltasar Garzon.
Garzon opened an investigation but under pressure from public prosecutors in 2010 passed jurisdiction down to regional courts before being tried for abuse of power for violating an amnesty agreed in 1977 as Spain moved towards democracy two years after General Francisco Franco's death by opening the probe.
"Since then courts have shelved the complaints without carrying out any type of investigation," said Esteban Beltran, the director of Amnesty International's branch in Spain.
The amnesty law, which was approved by parliament, covers all crimes of a political nature committed before 1977 "whatever their outcome."
That stance was seen as a necessity by the leaders tasked with unifying the country still smarting from the wounds of the civil war and dictatorship and protect officials from score-settling.
Unable to seek justice in Spain, about 50 Spaniards have brought charges in Argentina for crimes against humanity against the four policemen they say tortured them during the Franco era.
Argentine federal judge Maria Servini de Cubria has agreed to hear the case under the doctrine of "universal jurisdiction" which allows courts to try cases of human rights abuses committed in other countries.
Last month she issued arrest and extradition orders for the four policemen, two of whom are alive and living in Spain.
"When the doors were closed here, we thought of the principle of universal jurisdiction and we turned to Argentina," said Silva, whose grandfather was shot by Franco's forces in 1936 near Leon in northwestern Spain.
But the Spanish government has not cooperated with the Argentine investigation.
A bid by Servini to question Spanish victims by video conference was blocked earlier this year by the Spanish government.
And three weeks after she issued her arrest and extradition orders, the two policeman remain at large.
Daily newspaper El Mundo published a photo on Sunday of one of two, 67-year-old Juan Antonio Gonzalez who it described as "the most feared inspector of Franco's political police", as he took part in a recent marathon in Madrid.
Nearly four decades after Spain's amnesty law was passed, both the ruling conservative Popular Party and the main opposition Socialist Party, reject repealing the amnesty.
"We do not back changing that commitment which established a political agreement to not make mutual recriminations about the past," said former Socialist cabinet minister Ramon Juaregui, who warned of the "danger or returning the country to a fratricidal controversy".
The UN, which sent a working group to Spain to see how the country was investigating Franco-era disappearances, last month urged Madrid to overturn the amnesty.
"The amnesty can't serve as a barrier to the investigation of serious human rights violations," said Ariel Dulitzky, a member of the UN working group which spent a week in Spain interviewing hundreds of family members of those who disappeared.
"We believe the Spanish government, through its judiciary, should try the forced disappearances," he added.
Garzon, who was disbarred as a judge by Spain's Supreme Court in 2012 for illegally recording defence lawyers' conversations with clients, argued international laws against the worst human rights violations should trump the national amnesty.
The Popular Party, which traces its origins to the Popular Alliance, a union of seven conservative political parties formed in the 1970s by Manuel Fraga, a long-time cabinet member under Franco, is reluctant to act because of its historical ties to the dictatorship, said Fermin Bouza, a sociologist at Madrid's Complutense University.
"The government is of the right and it is a government that comes from that regime, in that sense it is normal that they have that reluctance," he said.
Justice Minister Alberto Ruiz Gallardon, whose father-in-law was a cabinet minister in the Franco regime, recently defended the amnesty law in parliament, calling it "the only consistent policy that can end this past of civil war and crusades."