The conviction of two former dictators for the systematic stealing of babies from political prisoners 30 years ago is a big step in Argentina's effort to punish that era's human rights abuses, though certainly not the last.

Following Thursday's convictions of Rafael Videla and Reynaldo Bignone, at least 17 other major cases are before judges or are nearing trial.

Among them is a "mega-trial" involving the Navy Mechanics School, which became a feared torture center as the 1976-1983 military junta kidnapped and killed 13,000 opponents while trying to annihilate an armed leftist uprising. That case involves 65 defendants, nearly 900 victims, more than 100 witnesses and about 60,000 pages of evidence.

Inspired by the Cuban revolution and Salvador Allende's socialist presidency in Chile, leftist idealists across Latin America debated in the 1970s about how best to change their countries _ through armed revolution or elections. With Allende's death during the 1973 coup of Gen. Augusto Pinochet, a hard core of activists figured guerrilla war was their only alternative, and carried out a series of ransom kidnappings, hijackings, assassinations and bombings.

Argentina's insurgents alone killed hundreds of military and police officers, right-wing politicians and executives of foreign-owned companies. Fearing outright civil war, military dictatorships took over much of the continent, and with the support of the United States government, imposed what Latin leaders now describe as regimes of state-sponsored terror.

Just before she was ousted by Argentina's military in 1976, President Isabel Peron decreed that leftist subversives must be "annihilated" to crush even the threat of armed revolution.

Still, Argentina's baby thefts set its junta apart. No other military regime in Latin America went to such lengths to remove traces of the political prisoners they captured and killed.

A "Never Again" commission formed shortly after Argentina's democracy was restored in 1983 documented thousands of crimes against humanity during the military regime, but hardly any of the violators were prosecuted until the late Nestor Kirchner was elected president 20 years later.

Justice Minister Julio Alak said Thursday that Kirchner's wife and successor, President Cristina Fernandez, deserves credit for making the human rights cases a cornerstone of government.

"It's unthinkable that in a state of law, the murderers of the people could be in any place but prison," Alak said after the verdicts were read.

Videla, 86, was sentenced to 50 years in prison, while the 84-year-old Bignone got 15 years, adding to the life sentences both men already had for other crimes against humanity. Seven co-defendants also were convicted, and two were acquitted by a three-judge panel.

While the dictators are behind bars, most defendants convicted of rights violations remain free on appeal, and many others have yet to stand trial.

According to a March tally by Argentina's independent Center for Legal and Social Studies, a total of 1,861 defendants have been named in cases of state terror, but verdicts were reached for only 17 percent of them _ with 92 percent of these found guilty. Since the trials began in 2006, at least 65 have resulted in sentences, but only seven cases have exhausted an appeals process that takes more than two years on average.

Still, Thursday's verdicts were a cause for celebration outside the federal courthouse in Buenos Aires, where activists watched them being announced on a huge television screen.

"This is an historic day. Today legal justice has been made real _ never again the justice of one's own hands," prominent rights activist Tati Almeida said.

Many pregnant prisoners were "disappeared" shortly after giving birth in clandestine maternity wards, their babies handed over to trusted military and police families.

Still, Videla testified that there was no systematic program for stealing babies, and accused prisoners of using their unborn children as "human shields."

He called himself a "political prisoner," and characterized his sentence as farcical act of revenge by people who after being defeated militarily now occupy positions in the government. But Videla said he would accept his sentence "in protest, as an act of service," and with a clear conscience.

Witnesses included former U.S. diplomat Elliot Abrams. He was called to testify after a memo describing his secret meeting with Argentina's ambassador was declassified at the request of the Grandmothers of the Plaza de Mayo, a rights group whose evidence-gathering efforts were key to the prosecution.

Abrams said he secretly urged that Bignone reveal the children's identities as a way to smooth Argentina's return to democracy.

"We knew that it wasn't just one or two children," Abrams testified, suggesting that there must have been a plan directed from a high level to handle the prisoner's babies.

Instead, Bignone ordered the military to destroy evidence of "dirty war" activities, and the junta denied any knowledge of baby thefts. The U.S. government also revealed little of what it knew at the time when junta death squads were eliminating opponents.

The Grandmothers have since helped 106 people recover their true identities through DNA testing, and 26 of these cases were part of this trial. As many as 400 other young adults could be out there still, the Grandmothers say, but it's impossible to know for sure.

The trial featured gut-wrenching testimony from relatives who searched inconsolably for their missing children, and from young adults who recently learned that they were raised by some of the very people involved in the disappearance of their birth parents.

The other sentences included former Adm. Antonio Vanek, 40 years; former marine Jorge "Tigre" Acosta, 30; former Gen. Santiago Omar Riveros, 20; former navy prefect Juan Antonio Azic, 14; and Dr. Jorge Magnacco, who witnesses said handled some of the births, 10.

Former Capt. Victor Gallo and his ex-wife Susana Colombo were sentenced to 15 and five years in jail, respectively, after their adopted son, now going by his original birth name Francisco Madariaga, testified against them.

Retired Adm. Ruben Omar Franco and Eduardo Ruffo, a former intelligence agent accused of handing Madariago over to Gallo, were absolved.

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Associated Press writer Debora Rey contributed to this report.