For years, Mr Gonzalez insisted he knew nothing about illegal undercover hit-squads, organised, armed and funded by the Spanish interior ministry soon after his Socialist government came to power.
Mr Gonzalez's appearance before 11 Supreme Court judges marks a watershed, 15 years after the anti-terrorist Liberation Groups, the Gal, launched a spate of kidnappings, torture and assassinations in a desperate attempt to crush Basque separatist terrorism.
Of the 27 killed by Gal mercenaries, perhaps half were not terrorists, Eta sympathisers or even Basque.
Despite his denials, suspicions about Mr Gonzalez's possible involvement produced the most serious and persistent scandal of his 14-year government and contributed greatly to his defeat in the elections in March 1996.
He has since stepped down as Socialist party leader, but he appears on the point of pitching for the presidency of the European Commission to succeed Jacques Santer next year.
Mr Gonzalez himself has not been charged. The main man in the prosecutor's sights is his former interior minister, Jose Barrionuevo, who faces 23 years in jail if he is found guilty of the charges of belonging to an armed group, kidnapping, and misappropriating public funds.
But it would be inconceivable for Mr Gonzalez to be considered seriously for an important international post if his political record was not considered squeaky clean.
The case against Mr Barrionuevo, his deputy, Rafael Vera, and a clutch of security chiefs and policemen who masterminded law and order operations in Spain for years, focuses on the Gal's first acknowledged action, the botched kidnap of a French businessman in December 1983.
The mercenaries who seized Segundo Marey realised within hours that they had the wrong man - they mistook him for an Eta leader - but he was held blindfolded in a ruined farmhouse in northern Spain for 10 days before being dumped across the border in France.
Mr Barrionuevo insists he is innocent of any illegal anti-terrorist activities, but, strangely, he said he would consider taking the rap if his subordinates were pardoned.
Nine co-defendents admit taking part in Gal actions - some have been convicted for other Gal crimes - but say they were following interior ministry orders.
At least one alleges that Mr Gonzalez was kept fully informed. Mr Barrionuevo's willingness to take responsibility could rebound against Mr Gonzalez. If the former interior minister is found guilty, might not the finger point to his boss?
Meanwhile, in Brussels, Mr Gonzalez's supporters are moving quietly into action.
His reputation in Europe is based on his leading Spain into the EU in 1986, sealing the country's transition to democracy.
Four years ago, Helmut Kohl urged him to accept the job as Commission president, but Mr Gonzalez instead fought unsuccessfully for a fifth term as Spain's prime minister.
The former Commission president Jacques Delors has proposed that parties nominate their preferred candidate before the European parliament elections next June. The Socialists are by far the strongest group and Mr Gonzalez is well placed to be their choice.
The appointment is likely to be made at the EU summit in June 1999, chaired by Germany, where either Mr Kohl or his possible socialist successor Gerhard Schroder would give Mr Gonzalez a fair wind.Reuse content