1. Identification of unknown deceased in Mexico

In Mexico, violence and crime have increased since the beginning of the “War on Drugs” in 2006 [1], accompanied by rising numbers of homicides that are often linked to drug-trafficking groups [2]. Furthermore, the National Registry of Missing and Unlocated Persons (Mexico) has been counting an increasing number of missing people from 2006 until today [3]. A total of 113,574 people are currently reported missing in Mexico and cannot be located. Almost every day, unknown dead bodies are found and delivered to Mexican Forensic Medical Services for identification. They may come from hidden mass graves that are frequently found by authorities or searching relatives. In more than a few cases, the bodies not only show signs of advanced decomposition, but also have been dismembered, burned, or treated with acid to complicate the identification process. Combined with financial and personal shortage, this vast number of bodies to be identified is a major burden for laboratories, authorities, and the society.

2. German-Mexican International Collaboration

Project “CoCiMex” (DAAD)

The CoCiMex project [4] was founded in 2021 as German-Mexican University Collaboration to support the Mexican Forensic Medical Services in the identification process of unknown deceased in Mexico. The Institute of Legal Medicine Frankfurt, Germany, was among others part of this project. The research project was supported by the German Academic Exchange Service (DAAD) with funds from the German Cooperation for Sustainable Development GmbH (GIZ) on behalf of the German Federal Foreign Office (DAAD Project ID: 57594060).

Project “ID-Mex” (UNFPA)

As follow-up project after the end of the CoCiMex cooperation, the United Nations Population Fund (UNFPA) and Goethe University Frankfurt am Main signed a cooperation agreement at the end of June 2023 to support the Mexican government in identifying unknown bodies in Mexico. The current project is called ID-Mex “Identification in Mexico”.

Which Tissue to Take?

During a research stay in Mexico as part of the CoCiMex project (DAAD), DNA samples from body parts that have been exhumed from a hidden mass grave were taken, including bone, teeth, hair, nail, tendon, muscle, and no longer differentiable soft tissue. DNA had to be extracted from body parts with heavy postmortem changes and, for different reasons, indeterminate storage conditions. Our laboratory was faced with a new challenge since we had rarely worked with such degraded tissues. The question was: Which tissue is most appropriate for DNA analysis while also considering time and cost efficiencies. Solid material such as teeth or bones are the gold standard as DNA material for genetic analysis of altered human remains, but the analysis is time- and cost consuming [5]. Different tissues such as kidney, liver, skeletal muscle, cartilage, intervertebral discs, and Achilles tendons were tested as alternative DNA material, proposed, and approved for DNA analysis of samples with an extended post-mortem interval. However, there are always cases in which the above-mentioned tissues cannot be used due to the decomposition of the corpses or simply because the body part to be examined has no nails, liver, or kidney. We wanted to explore if tendons could serve as a potential alternative DNA source, since tendons are present in every part of the body and can be easily collected and extracted without time-consuming sample preparation as in the case of bones. Our efforts focused on improving DNA extraction from bone and tendon samples using the Maxwell® FSC DNA IQ™ Casework Kit.