MADRID—Thousands of protesters, including artists, politicians and union members, marched in downtown Madrid on Sunday in support of a judge who is on trial for allegedly overstepping his jurisdiction by probing atrocities stemming from Spain's civil war.

Baltasar Garzon became an international human rights hero when he indicted former Chilean dictator Augusto Pinochet in 1998 and al-Qaida leader Osama bin Laden in 2003. But he ran into trouble for trying to investigate deaths and disappearances during and after the 1936-39 war which brought dictator Gen. Francisco Franco to power.

Garzon is on trial in the Supreme Court on three counts of allegedly giving legal instructions that he knew were unlawful.

Spaniards are highly divided over Garzon -- he has rock star status among human rights groups but conservatives deride him as being more interested in fame than justice. The marchers Sunday chanted and carried banners that read: "Garzon, friend, Spain is with you."

Retired printer Raul Ruiz, 69, carried a placard with a cartoon showing a judge presenting Garzon's head on a platter to Franco, who ruled from 1939 till his death in 1975.

More than 100,000 noncombatant civilians died or disappeared at the hands of Franco supporters, but crimes that took place during his dictatorship are covered by an amnesty passed in 1977 as Spain strove for a consensus to restore democracy.

"It is unjust to try a judge, whose job is to investigate crimes, for looking into cases simply because they are controversial," singer-songwriter Raul Anoz said.

Store owner Monica Garcia, 46, said she was ashamed by how her country was treating Garzon. "Fascist murderers were tried in Germany, but here in Spain, Franco's murderous dictatorship has for decades remained un-investigated and unpunished," Garcia said.

Ignacio Fernandez Toxo, 59, head of the Workers Commissions union, said his members were indignant that no one had so far asked the Fascist dictatorship to account for its crimes. "Then, when a judge begins look into it, he gets taken to court," he said.

If found guilty, Garzon -- who was suspended from his job at the National Court in 2010 in advance of the cases -- can be disbarred for up to 20 years. The decision would effectively end his career.

The cases stem from a complaint filed by the leaders of two right-wing groups, even though government prosecutors themselves say Garzon did nothing wrong and should be acquitted.

By a quirk of Spanish penal law, private citizens can seek to bring criminal charges against someone even if prosecutors disagree.

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