An Investigation Into The Interpretation Of Hair Evidence In Casework

The microscopic analysis of hair evidence is a technique that has been utilised for forensic purposes for over a century. This involves using microscopic methods to observe the external and internal characteristics that make up a hair. In recent years, this method has been criticised heavily for its subjective nature and lack of valid and standardised methods of analysis and interpretation. As a result of this, the use and reputation of hair evidence has greatly reduced.

The aims of this thesis were to investigate the current methods of analysis and interpretation of hair evidence in casework on an international scale, to design new approaches for objective hair observations and data generation, and to investigate the competency of the new approach and to make recommendations for future use.

These aims were met using a number of methods. Firstly, the current methods of analysis and interpretation were investigated by carrying out an extensive literature review to identify gaps in research and conducting a survey and subsequent follow up interviews with hair examiners to assess what is currently being performed in casework. New approaches for the assessment of the critical interpretation issue of inter and intra variation in hair samples was assessed by creating a reference sample collection, assessing the characteristics present within these, and applying a simple 6-point grading scheme and statistical methods to identify the level of variation present between and within individuals. Two new objective approaches were then created for the analysis of hair samples which utilised grading schemes. The initial grading scheme focussed on investigating heat damage in hair samples. As this was successful, this grading scheme style was then applied to the general approach of hair analysis and interpretation and converted many of the qualitative characteristics into a quantitative and more objective grading scale. This grading scale was then trialled on undergraduate students to identify its suitability for training purposes and then using hair examiners to identify if this is fit for purpose in casework.

From the assessment of the current status of hair analysis, it was identified that improvements have been made in terms of the use of proficiency testing and guidelines however there is a lack of standardised methods in place for the analysis and interpretation of hair evidence. The level of variation was identified in hair samples taken from a small set of donors but demonstrated that variation is present at both the inter and intra level, but these levels are higher for intervariation therefore allowing some discrimination between individuals. The use of a grading scheme to assess the level of heat damage in hairs was successful so was therefore developed for the general hair analysis process. Many of the typically qualitative characteristics used in hair comparisons could be converted into a numeric grading scale and when trialled, hair examiners made less incorrect associations using this method than those who used their current approaches.

This research has added to the knowledge base of forensic hair analysis with information concerning the current status of the analysis and interpretation of hair evidence along with providing novel information concerning the inter and intra variation present in hairs to be used to aid in the interpretation of casework and has provided a new structured approach to the analysis and interpretation of hair evidence. Previous reports have stated the issues surrounding hair analysis, however little research has been carried out to assess if these issues are still present in practice. This research has addressed this gap of knowledge by identifying how practice has improved and what issues are still prevalent. The issue of intravariation has been widely stated as a common problem when making interpretations but the actual level of variation has not been quantified. However, this research has provided quantification of this type of data on a small dataset allowing a starting point for a more large-scale study to be carried out which would provide the justice system with actual data on how this issue affects a conclusion. Although reports have stated that a structured approach is needed, this study has shown the benefits of applying a structured approach to hair examination i.e. a more conservative approach is used with less false positive conclusions made.