"Señora, go and search for yourself." With those words, Mexican authorities sent away the grieving mother seeking clues about her daughter's killer. The year was 2001, after those authorities had discovered the bodies of eight young women in a cotton field near Ciudad Juárez on the Texas-Mexico border, across the Rio Grande from the U.S. city of El Paso. Police were unlikely to solve their cases, just like those of the hundreds of women who had been sexually abused, mutilated and killed in this lawless town, where this year alone another 60 women and girls have been murdered. The government's handling of the "Campo Algodonero" murders stood out as an egregious violation of human rights for the way the authorities botched the case and mishandled the women's remains.

The victims' mothers even came to doubt that the remains authorities had given them were their own children. In December 2003 they began working with Mercedes Doretti, a New York-based forensic anthropologist and co-founder of the Argentine Forensic Anthropology Team to get help in identifying the bodies.

Doretti's work in Ciudad Juárez revealed that law enforcement had misidentified three of the eight remains furnished, and her report to the Inter-American Court of Human Rights led in 2009 to an order for reparations to all the families and a condemnation of the Mexican justice system. That small victory cemented Doretti's resolve to probe deeper. She now knew that dozens of other bodies had no possible matches to local families. Where had these other victims come from?

Doretti, a stylish woman in her 50s, has spent her life supporting human rights. She studied anthropology in Buenos Aires, during the height of Argentina's "Dirty War," when the right-wing regime kidnapped, tortured and murdered some 20,000 students, activists, journalists and guerrillas. Her team's work identifying remains of the Desaparecidos—the disappeared ones—continues today, and evidence she personally collected in the 1980s is still making its way through the country's legal system. In 2007 the MacArthur Foundation awarded her a "genius grant" for her work investigating human rights abuses around the world, and she serves as a Chairman of the Board of Trustees of the United Nations Voluntary Fund for Victims of Torture.

Doretti suspected that some of the unidentified bodies in Mexico may have been migrants journeying north from Central America, and in 2009 she established the Missing Migrants project. The full scope of the problem is hard to pin down, but some 200 migrants die of exposure each summer in southern Arizona alone. Mexico's criminal gangs have kidnapped many more for extortion or murdered and buried these victims in mass graves. Doretti has created a network of forensic DNA banks in El Salvador, Honduras and Chiapas, Mexico and recently announced her first positive identifications from remains recovered in Texas and Arizona. "It's amazing what she's doing," says Bruce Anderson, forensic anthropologist with the medical examiner's office in Pima County, Arizona.

Scientific American met Doretti at her organization's spartan one-room office in Brooklyn's DUMBO neighborhood. Edited excerpts follow.

When the Argentinean dictatorship collapsed in 1982, you still thought that you might follow an academic anthropology path. How did you get introduced to forensics?
I was at a demonstration against the International Monetary Fund in January 1984, and one of my friends came and said: "There's a gringo who wants to exhume disappeared people." As it happened, the American Association for the Advancement of Science had sent a scientist named Clyde Snow down to train people in forensics, but the Argentinean Anthropology Association initially did not want to get involved directly. Snow didn't have anybody to work with. Frankly, it sounded very strange to me. But after meeting him the next day, I realized everything he was saying made total sense—to apply the techniques of traditional archaeology and biological anthropology into the forensic field so that we will be able to recover and identify the remains of Los Desaparecidos in the proper way.

Were you afraid of the consequences of working on a politically charged project like this?
I was very scared. If you look at the history of Argentina, there had been a coup of every democratic government since the 1930s. If there was another coup we knew we would probably have to leave the country. Also, none of us knew how we were going to react personally when entering a cemetery. It's very different to dig up remains 10,000 years old than to dig up recent remains. We would also be working surrounded by the police, who brought back terrible memories from the dictatorship.

Was your family affected by the dictatorship?
Yes, though not in the way in which other families were affected. We didn't lose any members of our family, but because my mother worked as a journalist and was talking about these things on her daily radio show, she was constantly receiving death threats. We thought about leaving the country.

Several days after meeting Snow, you began your work at a cemetery as part of a judicial investigation. What was the condition of the first remains you uncovered?
They were fully skeletonized and, to my surprise, I was able to cope. I was very concentrated on the details of digging and cleaning the skull and making sure that the teeth didn't fall out and things like that.

This was before DNA was commonly used in forensics, so how did you make identifications?
The early identifications were done using dental records, X-rays and fingerprints. In Argentina, disappearances were conducted in a clandestine way until the moment of death. The bodies would be disposed of in secret graves inside military or police compounds, by dumping them out of airplanes or in vacant lots. In this last case, often then, someone would place an anonymous call to the police reporting their location, and everything would subsequently be done in a bureaucratic, official way. The police would take fingerprints and photographs. Forensic doctors would do autopsies, issue death certificates. The registration office will issue burial certificates, and then they bury them as John Does or Jane Does in municipal cemeteries.

One of the unique features of the Argentinian team is that you investigate only if family members of the missing give you permission, and then the families remain involved in the process.
Something we've seen in every country where we've been is that in human rights cases the families had a very tense relationship with official forensic experts. There had been cases in which doctors have actively participated with the police during torture or changing or obscuring death certificates. For example, they would say someone died of cardiac arrest but then when we exhumed the body, it has five bullets in it.

In the U.S., family members can be among the suspects of a crime. That's not the case in most human rights investigations we've participated in, but the families are normally being harassed, misinformed and stigmatized by officials, by society and so on because of what happened to them. They don't need any more of that. We often find ourselves having to review cases not necessarily because the results are wrong, but because the relationship between the officials and the families are so bad.

We realized we have to be extremely transparent with relatives of human rights victims. We have to tell them what we're finding as long as they want to know; it's their right. So little by little, without actually having that as a goal, we started to develop this approach of working in a very close relationship with family.

How have genetic technologies changed the way you work?
Enormously. The people who disappeared in Argentina, they were almost all in their 20s and early 30s and pretty healthy, so it was very hard to find features that distinguished them. We started using mitochondrial DNA in the 1990s but were only doing three or four cases a year with the pro bono work of U.S. and U.K. laboratories. After the Bosnian War and the World Trade Center attacks, forensic DNA technologies became much cheaper, faster and more accessible. We joined with teams in Peru and Guatemala to put together a project called the Latin American Initiative for the Identification of the Disappeared and got funding from [the] U.S. Congress in 2008. This allowed us to start our own DNA laboratory and send other bone samples to the same laboratory that processed the remains from the World Trade Center. We have gotten nearly 518 positive identifications, always through a multidisciplinary approach but where often genetics has been crucial, and we have about 750 still to be identified.

In 1992, you opened the team's New York office and began working on more international projects. What has been the biggest obstacle to expanding these approaches to human rights investigations around the world?
The main problem is always access. If there isn't the political will to investigate a crime, you may have all the evidence in the world, you may have all the experts, all the funding, but you're not going to be able to do it.

That's a good summary of the Campo Algodonero case in Mexico. How did you become involved in that project?
The case involved analysis of seven of eight female remains found in 2011 [in] a cotton field in the outskirts of Ciudad Juárez. We worked on this case at the request of families that had doubts about the identification of the remains they had received from the prosecutor's office. In fact some of them had so much doubt that they did not collect the remains from the morgue. Others decided they should just keep the remains and preserve them for a time when it could be investigated better. This case was part of a larger project to examine unidentified remains dating back to 1993.

What problems did you find with the Mexican forensic investigation of this case?
In some cases, Mexican laboratories were just not that experienced on doing DNA on bone samples, but in other cases I think there was willful misconduct. These remains had gone through several DNA analyses in Mexican state and federal laboratories, and they came back with different results. It was one of the few places in the world where we arrived and the families said, "We don't trust DNA." There were other problems as well. Some forensic experts produced results based on anthropological techniques that contradicted most of the DNA results. Some of the remains were not with their original clothing—they had male clothing on them. In one case most of the biological and documental evidence had disappeared—we found the spine at the medical school.

So what we did was start from scratch. We read all the different forensic results for the eight cases. We ran new DNA tests of the eight bodies, comparing them not only against these eight families but against 75 families that were part of a larger DNA database of missing women. This is how we confirmed some of the original identification and found misidentifications as well.

How did spending time in the border region introduce you to the plight of immigrants?
Working in Juárez was very hard—hard to get the information, hard to get the files and hard because of direct obstruction from officials. At the end of our work there, we had 50 female remains that did not match any of our families. So we thought these girls must be coming from somewhere else, either from another state in Mexico or from Central America, but there was really no fluid, efficient mechanism in place to exchange data with these places.

How have you tried to solve the problem?
What we are trying to do with the Missing Migrants program that we started in 2009 is improve the search of missing migrants among unidentified remains by creating a regional exchange system. We take background information interviews with the families to know when the migrant left; when was the last time that that person called; what else the family found out after that person stopped calling; what was the route that the person was thinking of taking; were they planning to cross by Arizona, by Texas, by California; was that person going with other people or just by themselves. Then, we collect the antemortem information—the classic dental information, fracture data, anything that can happen to them in life.

Previously, in most of these cases, unless there was a specific hypothesis related to a body, families were not asked to provide blood samples. There isn't a regional system, and a lot of people were not getting identified. We are setting up forensic banks in El Salvador, Honduras and Chiapas, Mexico, to collect background and physical information about missing migrants as well as blood samples from relatives. Each family will now have its forensic file ready to be considered against any morgue or place that has remains in the U.S. or Mexico. There was nothing like this before.

What is the biggest scientific challenge to identifying the remains of migrants?
Because these migrant cases involve people from several countries where we don't know yet how large the problem is, even with the support of DNA, it is often complex to distinguish between a random and a real match, which creates several technical and practical challenges. We have to test as many relevant relatives per family as possible and often perform complementary and additional genetic testing, combined with background and antemortem data to see if an initial genetic result is random or biologically significant. We now have 710 relatives tested in Chiapas, Honduras and El Salvador corresponding to 272 missing migrants.

You're even testing relatives here in the U.S.
Yes, the rhythm of this office has changed. Families here in New York or in the United States now call about once a week and tell us, "My daughter, my son, whoever, has disappeared and are missing."

How many remains have you identified from these families living in America?
We have identified eight from Arizona and one from Texas, with five more in process. We are just starting to exchange information. The main goal is to provide a better service to families who have a missing migrant. That's the main thing—to respect them, to be transparent and to provide them with the best available technology that exists.

Brendan Borrell is a writer based in New York City and is researching the plight of missing migrants with a grant from Investigative Reporters and Editors.