It took an incessant search by a human rights group, a DNA match and almost a decade of overcoming denial for Ms. Montenegro, 35, to realize that Colonel Tetzlaff was, in fact, not her father — nor the hero he portrayed himself to be.

Instead, he was the man responsible for murdering her real parents and illegally taking her as his own child, she said.

He confessed to her what he had done in 2000, Ms. Montenegro said. But it was not until she testified at a trial here last spring that she finally came to grips with her past, shedding once and for all the name that Colonel Tetzlaff and his wife had given her — María Sol — after falsifying her birth records.

The trial, in the final phase of hearing testimony, could prove for the first time that the nation’s top military leaders engaged in a systematic plan to steal babies from perceived enemies of the government.

Jorge Rafael Videla, who led the military duringArgentina’s dictatorship, stands accused of leading the effort to take babies from mothers in clandestine detention centers and give them to military or security officials, or even to third parties, on the condition that the new parents hide the true identities. Mr. Videla is one of 11 officials on trial for 35 acts of illegal appropriation of minors.

The trial is also revealing the complicity of civilians, including judges and officials of the Roman Catholic Church.

The abduction of an estimated 500 babies was one of the most traumatic chapters of the military dictatorship that ruled Argentina from 1976 to 1983. The frantic effort by mothers and grandmothers to locate their missing children has never let up. It was the one issue that civilian presidents elected after 1983 did not excuse the military for, even as amnesty was granted for other “dirty war” crimes.

“Even the many Argentines who considered the amnesty a necessary evil were unwilling to forgive the military for this,” said José Miguel Vivanco, the Americas director forHuman Rights Watch.

In Latin America, the baby thefts were largely unique to Argentina’s dictatorship, Mr. Vivanco said. There was no such effort in neighboring Chile’s 17-year dictatorship.

One notable difference was the role of the Catholic Church. In Argentina the church largely supported the military government, while in Chile it confronted the government of Gen. Augusto Pinochet and sought to expose its human rights crimes, Mr. Vivanco said.

Priests and bishops in Argentina justified their support of the government on national security concerns, and defended the taking of children as a way to ensure they were not “contaminated” by leftist enemies of the military, said Adolfo Pérez Esquivel, a Nobel Prize-winning human rights advocate who has investigated dozens of disappearances and testified at the trial last month.

Ms. Montenegro contended: “They thought they were doing something Christian to baptize us and give us the chance to be better people than our parents. They thought and felt they were saving our lives.”

Church officials in Argentina and at the Vatican declined to answer questions about their knowledge of or involvement in the covert adoptions.

For many years, the search for the missing children was largely futile. But that has changed in the past decade thanks to more government support, advanced forensic technology and a growing genetic data bank from years of testing. The latest adoptee to recover her real identity, Laura Reinhold Siver, brought the total number of recoveries to 105 in August.

Still, the process of accepting the truth can be long and tortuous. For years, Ms. Montenegro rejected efforts by officials and advocates to discover her true identity. From a young age, she received a “strong ideological education” from Colonel Tetzlaff, an army officer at a secret detention center.

If she picked up a flier from leftists on the street, “he would sit me down for hours to tell me what the subversives had done to Argentina,” she said.

He took her along to a detention center where he spent hours discussing military operations with his fellow officers, “how they had killed people, tortured them,” she said.

“I grew up thinking that in Argentina there had been a war, and that our soldiers had gone to war to guarantee the democracy,” she said. “And that there were no disappeared people, that it was all a lie.”

She said he did not allow her to see movies about the “dirty war,” including “The Official Story,” the 1985 film about an upper-middle-class couple raising a girl taken from a family that was disappeared.

In 1992, when she was 15, Colonel Tetzlaff was detained briefly on suspicion of baby stealing. Five years later, a court informed Ms. Montenegro that she was not the biological child of Colonel Tetzlaff and his wife, she said.

“I was still convinced it was all a lie,” she said.

By 2000, Ms. Montenegro still believed her mission was to keep Colonel Tetzlaff out of prison. But she relented and gave a DNA sample. A judge then delivered jarring news: the test confirmed that she was the biological child of Hilda and Roque Montenegro, who had been active in the resistance. She learned that she and the Montenegros had been kidnapped when she was 13 days old.

At a restaurant over dinner, Colonel Tetzlaff confessed to Ms. Montenegro and her husband: He had headed the operation in which the Montenegros were tortured and killed, and had taken her in May 1976, when she was 4 months old.

“I can’t bear to say any more,” she said, choking up at the memory of the dinner.

A court convicted Colonel Tetzlaff in 2001 of illegally appropriating Ms. Montenegro. He went to prison, and Ms. Montenegro, still believing his actions during the dictatorship had been justified, visited him weekly until his death in 2003.

Slowly, she got to know her biological parents’ family.

“This was a process; it wasn’t one moment or one day when you erase everything and begin again,” she said. “You are not a machine that can be reset and restarted.”

It fell to her to tell her three sons that Colonel Tetzlaff was not the man they thought he was.

“He told them that their grandfather was a brave soldier, and I had to tell them that their grandfather was a murderer,” she said.

When she testified at the trial, she used her original name, Victoria, for the first time. “It was very liberating,” she said.

She says she still does not hate the Tetzlaffs. But “the heart doesn’t kidnap you, it doesn’t hide you, it doesn’t hurt you, it doesn’t lie to you all of your life,” she said. “Love is something else.”