But a quarter-century after Argentina's dictatorship and "dirty war" against its own citizens ended, DNA technology raises the possibility of finally learning the identities of these skeletons in the closet, collected from mostly unmarked graves across Argentina.
Anthropologists have launched an ambitious campaign, drawing on techniques pioneered in Bosnia and at New York's World Trade Center after the Sept. 11 attacks.
On television and radio, celebrities exhort relatives of "the disappeared" to provide blood samples for a nationwide DNA database. A weekday call center advertises its toll-free number on banners at soccer games.
"If you have a family member who was a victim of a forced disappearance ... a simple blood sample can help identify them," says a popular Argentine soccer sportscaster in a TV ad.
The campaign began in November and is already paying off.
"We've received some 2,000 telephone calls," said Luis Fondebrider of the independent Argentine Forensic Anthropology Team, which was founded in 1984 to document the missing and has since applied its know-how in more than 40 countries, from El Salvador to Iraq to East Timor. It also led the identification through dental records of Cuban revolutionary Ernest "Che" Guevara's remains, exhumed in the 1990s.
The nonprofit group hopes soon to recruit a U.S. lab to cross-match the samples with DNA from all 600 skeletons in the closet, many of which have bullet holes in their skulls or signs of torture.
Large-scale DNA sampling has become quicker and cheaper since it was pioneered in Bosnia, according to Mercedes Doretti, a founder of the group and a recipient of a 2007 MacArthur Foundation "genius grant."
After Bosnia's war in the early 1990s, the International Commission for Missing Persons developed a system to conduct sophisticated DNA tests on thousands of exhumed bodies.
After 9/11, U.S. experts expanded the technology, building software to compare thousands of DNA samples simultaneously from the fragments from the Twin Towers.
But Doretti's group did not have money to use these new technologies until the U.S. Congress gave it a grant last year of nearly US$1.5 million.
The Argentine government provides logistical support, arranges free air time for the advertisements, puts public blood banks at the group's disposal and speeds the importation of equipment through customs.
Adding to the urgency of identifying the dead, Argentina's new president, Cristina Fernandez, has pushed to speed up trials in hundreds of human rights cases that were blocked by an amnesty for alleged perpetrators. The amnesty was repealed in 2005.
The campaign could also lead to a more accurate death toll from the "dirty war" against leftist opponents by Argentina's 1976-83 dictatorship, and bridge the gap between the more than 12,000 officially listed as dead or missing and the 30,000 estimated by human rights groups.
"We hope there might be more people coming forward, especially in the provinces," to report missing relatives for the first time, said Luis Alen, a government undersecretary for human rights.
In most cases, victims' remains have never been found, and of those recovered by Doretti's group, fewer than 300 have been identified.
The last identification was in 2005, when DNA testing gave a name to remains that years earlier had washed ashore, apparently tossed from a "death flight" in which drugged prisoners were thrown alive into the sea. French nun Leonie Duquet was given an emotional funeral at the Buenos Aires church where she had been abducted in 1977.
Such matches were made by steadily improving DNA technology, which helped identify Hugo Omar Argente's brother Jorge, a youth activist whose body was among 30 dynamited after a 1976 massacre.
"They wanted to make the bodies disappear," said Argente, 55. "I found out on March 17, 2000, when they called me on the phone and said the test results had identified him. I just cried and cried."