Investigating current challenges in forensic ink analysis by Raman spectroscopy

Abstract

This Thesis emerged from the ongoing need to develop more scientifically based methodologies of investigation in Forensic Science in general, and Questioned Document Examinations in particular. Like in other fields of expertise, the methods for forensic ink analysis must be informative (i.e. add value to the forensic investigation), objective (i.e. independent of the examiner), robust (i.e. reproducible with respect to different examiners and institutions) and non§destructive of the documents evidential value. They also require to be validated under conditions reflecting those of the case under investigation and provide reliable results. Scientific and technological advances have been playing a crucial role in improving forensic investigations, but sometimes, the fundamental knowledge behind the nature of the evidence is overlooked. Therefore, the scope of the research described in this thesis was to build on the already existing knowledge and further investigate and develop the potential of Raman spectroscopy for current challenges related to forensic ink analysis. Considering this scope, this Thesis is organized into four chapters. The first chapter aims to introduce the forensic ink analysis in the context of Forensic Science and Questioned Document Examinations with the objective of providing the reader a better understanding of the concepts used throughout the Thesis. Due to the fact that Raman spectroscopy is an emerging technique in forensic ink analysis, the fundamental and instrumental features of this technique are given prior to a revision of the state of the art of Raman spectroscopy in this specific area of application. The second chapter of this Thesis (chapter 2) investigates the inter and intra brand, model and batch variability in the Raman spectral signature among blue pen inks with the final purpose of helping document examiners during the interpretation process of ink comparisons. The third chapter of this Thesis (chapter 3) investigates the ability of their Raman spectrometer for discriminating printing inkjet inks directly on paper. The research described in the last chapter of this Thesis (chapter 4) has two specific objectives. The first one was to build a more comprehensive understanding on how two inks distribute at the crossing, which involved investigating the several variables affecting the distribution of inks. The second was to develop innovative methodologies to determine the correct sequence of intersecting ink lines more effectively but also more objectively and whenever possible, non destructively.