Juan Guzman Tapia, a small-town judge in southern Chile, was on vacation in the seaside resort of Vina del Mar when his parents called to invite him over for champagne. It was Sept. 11, 1973, and the military had just overthrown President Salvador Allende, a socialist.

Like many affluent Chileans, Guzman and his family were relieved when Gen. Augusto Pinochet, the army chief, seized power. After a period of mounting leftist ferment, the upright army man vowed to restore order and expunge communism from Chile.

But 25 years later, as a judge in Santiago, Guzman glimpsed the horrors committed by Pinochet's secret intelligence apparatus, which had tortured and killed more than 3,000 people before leaving power in 1990. He probed into case after case, growing increasingly appalled and determined to bring the former dictator to justice.

The soft-spoken, erudite jurist became Pinochet's nightmare, questioning the aging general about the crimes of a military death squad, indicting him twice in rights abuse cases and lifting his immunity from prosecution four times.

"I understood that many people in my country had slept, like Rip Van Winkle -- a sleep of disinformation," Guzman, now 66, with a white beard and twinkling blue eyes, told an admiring audience at the National Press Club on Wednesday night.

He was there to receive a human rights award from the Institute for Policy Studies. The award is given annually in memory of Chilean diplomat Orlando Letelier, who was assassinated by agents of the Pinochet regime in a 1976 car bombing in Washington, together with an institute employee, Ronni Karpen Moffitt.

As Guzman received the award, Chile's Supreme Court stripped Pinochet of immunity from charges of tax fraud. The scandal stemmed from revelations that Pinochet and his family secretly held millions of dollars in overseas banks, including Washington-based Riggs National Bank.

In an interview Tuesday, Guzman described how he had unraveled some of the regime's dirtiest secrets, including an operation in which hundreds of prisoners were dumped from helicopters into the Pacific Ocean, after being stuffed into canvas sacks with their stomachs slit open and iron rails tied to their backs.

Guzman conducted forensic exams and interviewed mechanics and soldiers who had mopped up the blood in a secret provincial detention center. Eventually, he was able to detail 500 cases of "disappeared" individuals and indict one former director of the center -- his own cousin.

It was by twists of chance that Guzman, a self-described conservative with a gentle, literary air, became the tenacious prosecutor of a former dictator and his monstrous military machine.

As a boy he lived in San Francisco and Washington, where his father was a diplomat. Later, back in Chile, his parents' home was visited by such legendary figures as Chilean poet Pablo Neruda and Mexican painter Diego Rivera.

Guzman said he was an unenthusiastic law school student but later found his calling while clerking at a court in Santiago. In 1972, he applied for a judgeship and was sent to the town of Panguipulli, 500 miles south, where case files rotted and people swaggered into court as if entering a saloon.

Slowly he brought discipline and decorum to his chambers, arbitrating many cases of land seizures by peasants. Although he was "indifferent politically," he said, his support for the military coup helped him move up through the system to become a criminal court judge in Santiago.

But when he was shown photographs of petty thieves and beggars who had been tortured to death, he began to realize that military rule had perverted the system.

"I wanted to believe in the order that was being established, but I always voted against government decisions and for habeas corpus," he said. An amnesty law was promulgated by Pinochet to absolve the military from all crimes committed before 1978. Most judges, trained in a strict legalistic environment, simply shelved those cases.

Guzman next moved to an appeals court in the city of Talca, where he observed more military repression of the poor and his aversion to dictatorial rule deepened. But because he was outnumbered by pro-government judges on the panel, he acknowledged, "I became mute. You had to. I had no power to do anything."

In 1990, Chile finally held presidential elections and Pinochet was forced to step down, but the Supreme Court was still controlled by his allies. Over time, however, hundreds of abuse cases were filed against the former regime. At age 59, Guzman was chosen in a lottery to handle several major cases against Pinochet.

"I knew that second I would no longer be promoted," he said.

His superiors reprimanded him, but Guzman pressed ahead. Finally, by a careful but innovative interpretation of the law, he managed to reverse Pinochet's 1978 amnesty, ruling that as long as a body was missing, a case of disappearance could still be declared open.

"In one moment, he made the military vulnerable," said Peter Kornbluh of the nonprofit National Security Archive here.

In May, Guzman retired to dedicate his time to writing, and his memoir was recently published in Spanish. He said that he knows that the ailing Pinochet, 89, may never face trial but that he believes his own life's work is done.

"I was always a conservative with traditional democratic values, just a man of the law who respected order and the loyalty of armed forces towards a constitutional government," Guzman said modestly. "You see, I am no hero at all."

Juan Guzman Tapia prosecuted Gen. Pinochet.