The last witnesses took the stand Tuesday in defence of Baltasar Garzon, the Spanish judge on trial for attempting to investigate atrocities of the Franco era.

A leading campaigner for victims testified on behalf of his grandfather, who he says was murdered by the forces of Francisco Franco in Spain's Civil War, in a trial that has exposed the still-raw wounds from the period.

"What we want is for the courts to act as they do they for any crime," said Emilio Silva, who heads the national Association for the Recovery of Historical Memory.

"My grandfather was kidnapped, murdered and thrown into a ditch with two shots to the head," Silva told the Supreme Court, relating the killing in October 1936 at the beginning of the war.

Garzon, 56, who earned global prominence by trying to extradite Chilean dictator Augusto Pinochet from London in 1998, is accused of abuse of power for trying to investigate the atrocities despite an amnesty.

He says the acts were crimes against humanity and not covered by the amnesty, which was agreed in 1977 during Spain's transition to democracy after Franco's death.

The trial has outraged the families of people killed during the Civil War and Franco's subsequent dictatorship, prompting noisy protests outside the court.

Silva said the remains of his grandfather and several other people on the Republican side executed by the Francoist forces were identified by their DNA in a mass grave unearthed in 2000.

"My grandmother died without being able to talk about what happened to her husband," he told the court.

"The winners found and honoured the victims of the Marxist hordes, as they called the defeated side," he added.

"The losers were taught to keep quiet."

The trial enters its final day on Wednesday, when Garzon's final defence plea is due to be heard.

The public prosecutor has called for the case to be dismissed, but the court agreed to try Garzon in a suit brought against him by two right-wing groups.

If convicted of exceeding his authority Garzon could be suspended from the legal profession for 20 years.