REFLECTIVE SPECTROSCOPY STUDY OF BLOOD ON GEOLOGIC AND OTHER MATERIALS: PROVIDING FORENSIC CONTEXT FOR OUTDOOR CRIME SCENES

Violent crime, in which one or more persons are harmed or threatened with harm, can range in size from local crime to large scale political violence. One of the most important pieces of evidence that is often left at these crime scenes is residual blood. Proper detection and age estimation of blood found at crime scenes is crucial for forensic investigation. Hyperspectral analysis by examining unique absorption features is one such method of blood detection and age estimation. This hyperspectral work on blood has been done in the past, but not extensively with well-characterized geologic materials. The purpose of this study is to provide constraints and understand variability of blood aged on representative geologic substrates. This work can help forensics by verifying suspect identity, assisting in crime scene reconstruction, determining the elapsed time since a crime was committed and verifying testimonies through non-destructive techniques.

Two distinct substrate types were chosen, representative of a broad range of possible geographic areas within North America. Reflective spectroscopy analysis of blood on both of the sediment types was performed multiple times and averaged at 10 distinct periods of elapsed time, ranging from 1-144 hours, beginning when the blood first came into contact with the sediments. Graphs representing reflectance and corresponding wavelengths were generated for both sediment types at each of the 10 time periods. Unique absorption features relating to blood, such as Fe³⁺, were identified on each of the graphs. Changes in the detectability of certain absorption features relating to blood using reflective spectroscopy over this time period were documented.

This analysis provides frames of reference for future forensic investigations, utilizing reflective spectroscopy analysis of blood on similar geologic substrates, to assist in blood detection and aging. Using methods such as hyperspectral remote sensing, blood evidence can be found and documented in areas that would otherwise be difficult to gain access to, such as denied areas, countries, or ambiguous political borders. Further investigations into reflective spectroscopy detection and aging of blood on increased varieties of geologic material will provide greater context for future forensic investigations worldwide.