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Multi-isotopes in human hair: A tool to initiate cross-border collaboration in international cold-cases

NCJ Number
PLoS ONE Volume: 17 Issue: 10 Dated: 2022
Date Published

This study introduces a tool for screening human hair for multi-isotopes to facilitate cross-border cooperation in international cold-cases.


This study demonstrates that isotopic measurements are effective screening tools to help identify cold-cases with potential international ramifications. Unidentified human remains have historically been investigated nationally by law enforcement authorities. However, this approach is outdated in a globalized world with rapid transportation means, where humans easily move long distances across borders. Cross-border cooperation in solving cold-cases is rare due to political, administrative or technical challenges. It is fundamental to develop new tools to provide rapid and cost-effective leads for international cooperation. The authors first complete existing databases of hydrogen and sulfur isotopes in human hair from residents across North America by compiling or analyzing hair from Canada, the United States (US) and Mexico. Using these databases, the authors develop maps predicting isotope variations in human hair across North America. The authors demonstrate that both δ2H and δ34S values of human hair are highly predictable and display strong spatial patterns. Multi-isotope analysis combined with dual δ2H and δ34S geographic probability maps provide evidence for international travel in two case studies. In the first, the authors demonstrate that multi-isotope analysis in bulk hair of deceased border crossers found in the US, close to the Mexico-US border, help trace their last place of residence or travel back to specific regions of Mexico. These findings were validated by the subsequent identification of these individuals through the Pima County Office of the Medical Examiner in Tucson, Arizona. In the second case study, the authors demonstrate that sequential multi-isotope analysis along the hair strands of an unidentified individual found in Canada provides detailed insights into the international mobility of this individual during the last year of life. In both cases, isotope data provide strong leads towards international travel. (Published Abstract Provided)

Date Published: January 1, 2022