Telling the Stories of the Unidentified

Tara Luther, Promega

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While other girls her age were playing with dolls, Dr. Chelsey Juarez was jotting down notes about death and decomposition.

Growing up in the rural town of Gustine, California, she didn’t have neighbors for miles around, and access to television was limited, but she did live within walking distance to a dairy farm.

At 8 years-old, Dr. Juarez began to take notes about the cows who had perished and the changes that she observed during the decomposition process. As she grew to be a teenager, her interest also increased. She began to realize that there were clear stages of decomposition and began documenting them. It was then that she discovered her love for forensic anthropology, though she didn’t know it at the time.

Growing up in a small town, Dr. Juarez felt that her career options were already predetermined; she could become a dentist, doctor, lawyer, or veterinarian. She chose to become a doctor, however an internship at a free clinic quickly proved that this was not the best fit for her. She recalls that a doctor at the clinic noticed her distress. When she told him that working with living people and providing them with bad news gave her enormous stress, he suggested working with the dead instead. She enrolled in a forensic anthropology class and was hooked. As she sat in the front row each day, the work mesmerized her, and a new path began to solidify in front of her.

It wasn’t long before her passion for forensic anthropology began to intertwine with her ancestral roots. The daughter of a Mexican immigrant, Dr. Juarez always knew that she wanted to assist her Latino community, though she didn’t know what form that might take. As a freshman, she had immersed herself in the College of Chemistry and the lab at the University of California, Berkley, and was quite familiar with isotopes. Through her background in chemistry, she knew it was possible to track items like drugs, plant material, or even pottery across a landscape, and a question presented itself: could these isotopes also track human remains? Might she be able to assist in identifying border crossers who had perished?

The Nation’s Silent Mass Disaster

According to the National Missing and Unidentified Persons System (NamUs), 600,000 individuals go missing in the United States each year. While many are quickly found, it is estimated that 4,400 unidentified bodies are recovered each year, with 1,000 of them remaining unidentified after one year. All told, there are currently more than 40,000 sets of human remains listed as unidentified in the United States.

While advances in DNA technology have assisted in providing identities for many, limitations remain, especially with populations that are non-native to the United States. Many who have perished while attempting to migrate from Latin American countries have no genetic relatives in the United States, and they are undocumented. Those who may be relatives are hesitant to come forward to submit DNA, because they are also undocumented. Without reference samples to use for comparison, the power of DNA is limited.

Additionally, many of the remains found have been exposed to the elements for years. Often, little or no tissue exists, and the skeletons may be incomplete, which makes obtaining a DNA profile challenging.

Forensic Anthropologists as Storytellers

In cases where medical examiners are limited by the information that DNA analysis can provide, forensic anthropologists may be able to shed some light. As specialists in the hard tissues of the body, such as teeth, bones, fingernails, and even hair, forensic anthropologists tell the story of the deceased by providing a biological profile. This profile includes the sex, age, ancestry, living stature at the time of death, and a rough post-mortem interval. They are also able to determine if trauma or disease was present.

Once a biological profile has been completed, specially trained forensic anthropologists are able to perform an isotopic analysis to help determine where a person may have lived.

Isotopes are varieties of elements each with a different number of neutrons.
The varying number of neutrons leads to differing weights, which can be picked up through mass spectrometer analysis.

Isotopes vary depending on geographical location and may provide clues as to where a person was born, where they have recently lived, and where they were just months ago. When dealing with cold cases, this information can provide investigators with a place to start.

Traditionally, five different isotopes are used for forensic analysis. Hydrogen and Oxygen isotopes point to drinking water consumed. Carbon and Nitrogen isotopes provide information on a person’s diet. Finally, Strontium, which is found in both food and water, can suggest additional information about diet or local environments, depending on the tissues tested.

There are three main tissues tested, and each sheds light on a different stage of a person’s life. Teeth, such as the first molar, begin to form in utero and complete themselves by the time a person turns three. Performing an isotopic analysis on the oxygen levels within a tooth sheds light on where a person was born. Longer bones, like the femur, provide information on the past 20 years of a person’s life, while spongy bones like a rib or the cranium shed light on where someone has lived in the past five years. Finally, if you’d like to know where a person has been in the past several months, performing isotopic analysis on the oxygen levels of the hair or fingernails will be a great indicator.

Dr. Juarez provides more information on the process of isotopic analysis in the video below.

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Mapping Isotopes

The National DNA Index System (NDIS) currently contains 17.5 million offender DNA profiles that investigators can use to compare crime scene samples against. Forensic Anthropologists are working on developing a database as well, in the form of geographic isotope maps (‘isoscapes’). These maps, similar to the one below, show isotope levels by region.

Dr. Chelsey Juarez presents an isoscape of Strontium levels in Mexico at the 30th International Symposium on Human Identification

As Dr. Juarez started working with Latino immigrant populations, it became clear that she would need to collect samples from these regions for comparison. Through working with local dental clinics who served migrant populations, she was able to collect a number of donated teeth from those who had orthodontic procedures. Isotopic analysis on these teeth allowed her to begin to create reference maps.

Currently, while there are many isoscapes available, investigators are unable to layer the maps on top of each other in order to compare isotope types against one another. For instance, Strontium levels could be overlaid with Oxygen levels. Dr. Juarez tells ISHI that this will be coming soon.

How Can Isotopic Analysis Assist in Identifying Border Crossers?

Trying to identify immigrants who have perished is a complicated process, and isotopes are only one part of the puzzle. Dr. Juarez explains that it is helpful, and maybe even necessary, to involve a trans-border community in the identification process. This may include family members and consulate members from across the border.

She illustrates this point by sharing a case that she worked on while she was employed in North Carolina. Local authorities had discovered remains that were mostly skeletal and had hit a dead end with DNA analysis. They called Dr. Juarez for assistance. The deceased had three penetrating injuries to the skull and an x-ray showed a bullet lodged in the right maxilla. The biological profile showed that the deceased was a South American male, who was approximately 47 years of age. Dr. Juarez performed isotopic analysis of the tooth, femur, and rib. Oxygen levels from the tooth and femur came back the same, so she was able to conclude that the man had either lived where he was born for the majority of his life or had moved to a location with a similar water level as his birthplace. Strontium testing of the tooth and femur confirmed what the oxygen testing had shown, yet these levels did not match with the area where he had been found in Waite County. Ultimately, Dr. Juarez was able to conclude that the individual had migrated from Mexico and was able to work with the local Mexican consulate to help narrow down a possible identity.

Deceased, undocumented border-crossers from Latin America pose additional challenges when performing Oxygen and Hydrogen isotope analysis. The problem dates to the early 1900’s as Mexican states began to implement municipal water plans. Uneven development, poor water sanitation, damage from earthquakes, and deficiencies in repairs led to disparities in the ability to meet the need and water scarcity among Mexican states. Additionally, water-borne diseases such as cholera, amebiases, and cysticercosis, and over-chlorination have led to a loss of confidence in the municipal water. As a result, between 80-100% of Mexicans report using bottled water as their only source of drinking water, especially those under 40 years of age. According to Dr. Juarez, in addition to the large producers of bottled water, such as Coke or Pepsi, there are over 6,000 individual producers of bottled water across the country, and they are unregulated. This means that the bottled water consumed could originate from an entirely different state than where the drinker is living, which can lead to discrepancies in the isotopic analysis. To counteract this, researchers have begun to collect samples from available bottled water.

Much has changed for Dr. Juarez since those early days on the dairy farm, but her passion for forensic anthropology has only grown. Currently, she is working with Dr. Belinda Akpa from North Carolina State University to see if mathematical modeling would allow forensic anthropologists to predict isotope levels and a region of origin for a victim based on what is already known about a region, such as precipitation. Doing so may one day allow for the prediction of a migrational pathway based on different tissue samples available from a victim. Dialing in the modeling may one day allow investigators to determine the path an individual had taken, which could prove to be powerful in the fight against human trafficking and illegal immigration.

What would Dr. Juarez like to see for the future? “I think forensic anthropologists and our DNA colleagues need to work more together. I think that we have a lot to learn from you guys and we have something to offer in return. I think that if we can be more collaborative, then I think we can do some really awesome things.”

As for families who may have lost a loved one, Dr. Juarez has these words of comfort, “I hope that it never happens to you, but if you ever find yourself in a situation where someone that you care for or that you love goes missing, and you don’t know what happened to them, know that there are a lot of people that are working on cases just like this. They’re doing a lot of work behind the scenes, and they’re very dedicated forensic professionals. You have to be your own advocate for yourself and for your family, but there are a lot of people who are doing everything they can to make these identifications.”