Inocente Orlando Montano Morales, 77, was found guilty of "terrorist murder" for the killings which took place in November 1989 when the Jesuits were acting as a mediator to try to end the civil war between the government and FMLN guerrillas.

Spain's top criminal court said he was responsible for eight murders -- six Jesuits, one of whom was Salvadoran, their housekeeper and her teenage daughter -- but could only sentence him on the basis of five as it was on those grounds that he was extradited from the United States.

Speaking to reporters outside the court, lawyer Manuel Olle said the victims' relatives were "very satisfied" with the long-awaited ruling which established the truth about the past.

"At last we see justice has been done, impunity has been overcome, and the instigators who for so many years have prevented the truth from being known, have been unmasked," he said.

"The suffering of the Jesuit fathers, of the relatives and of all the Salvadoran people has been recognised."

The ruling was an "important step towards universal justice", Olle added, while expressing hope that El Salvador would now "start and resume trials that were once frustrated as a result of impunity".

- Gunned down -

The murders took place outside the priests' residence on the campus of the Central American University (UCA) in San Salvador, as the country was gripped by more than a decade of deadly fighting between government forces and the FMLN.

Among the victims was Spanish priest Father Ignacio Ellacuría, UCA's rector and one of the country's most important political analysts, the court said.

Three of the priests were shot as they lay on the ground, court documents showed.

Montano, who served as El Salvador's deputy minister for public security between 1989 to 1992, is the first to be tried over the bloodshed after Spain opened an investigation in 2009 on the principle of universal justice.

In 2011, a Spanish judge ordered the arrest of Morales and 19 other former Salvadoran soldiers for the murders.

El Salvador has refused to extradite the others to Spain, however.

- A guerrilla rifle -

Prosecutors said Morales gave the order for the killings, carried out early on November 16, 1989 with an AK-47 rifle that was often used by the FMLN, to pin the blame on the guerrillas.

Montano was extradited from the United States in 2017, where he had served nearly two years in jail for immigration fraud. Since arriving in Spain, he has been held in pre-trial detention.

He was due to be tried with Rene Yusshy Mendoza, a lieutenant in the Atlacatl counter-insurgency battalion that carried out the killings.

But when the trial opened in June, Mendoza was acquitted after the defence argued successfully that by the time he was charged, the statute of limitations had expired.

The civil war in El Salvador ended in 1992 after 12 years of fighting that left more than 75,000 people dead and 7,000 missing.