Large area imaging of forensic evidence with MA-XRF

Kirsten Langstraat,Gerda Edelman,Linda Van De Merwe,Joris Dik,Alwin Knijnenberg,Annelies Van Loon,Arian Van Asten

doi:10.1038/s41598-017-15468-5

Abstract

This study introduces the use of macroscopic X-ray fluorescence (MA-XRF) for the detection, classification and imaging of forensic traces over large object areas such as entire pieces of clothing and wall paneling. MA-XRF was sufficiently sensitive and selective to detect human biological traces like blood, semen, saliva, sweat and urine on fabric on the basis of Fe, Zn, K, Cl and Ca elemental signatures. With MA-XRF a new chemical contrast is introduced for human stain detection and this can provide a valuable alternative when the evidence item is challenging for conventional techniques. MA-XRF was also successfully employed for the chemical imaging and classification of gunshot residues (GSR). The full and non-invasive elemental mapping (Pb, Ba, Sr, K and Cl) of intact pieces of clothing allows for a detailed shooting incident reconstruction linking firearms and ammunition to point of impact and providing information on the shooting angle. In high resolution mode MA-XRF can even be used to provide information on the shooting order of different ammunition types. Finally, by using the surface penetration of X-rays we demonstrate that the lead signature of a bullet impact can be easily detected even if covered by multiple layers of wall paint or human blood.

Highlights

The introduction and use of macroscopic X-ray Fluorescence (MA-XRF) imaging has shown great value in the study of art objects[1,2,3]
The ability of macroscopic X-ray fluorescence (MA-XRF) imaging to detect biological traces of forensic relevance is mostly governed by its limited sensitivity in relation to relatively low levels of marker elements
MA-XRF detection limits for the elements of interest should be a factor of 10 lower (0.5–20 μg/cm2) to be able to confidently image the marker elements

Summary

Introduction

The introduction and use of macroscopic (or macro) X-ray Fluorescence (MA-XRF) imaging has shown great value in the study of art objects[1,2,3]. As alternative for the more invasive chemographic methods[21] for shooting distance estimation (important when investigating opposing scenarios, e.g. wrestling leading to an accidental gunshot versus a close-range execution) MA-XRF potentially provides valuable additional information for complex shooting incident reconstruction involving multiple firearms, ammunition types and shooters. This could even be the case in situations where perpetrators have attempted to conceal evidence at the scene in the aftermath of a crime. In situations where police officers have indications of crime concealment or covered traces, the use of MA-XRF as a mobile tool directly at the scene of crime could be an interesting future prospect

Methods

Results

Conclusion