The Problem of Efficiency of Microscopic Human Hair Analysis in the Forensic Biological Examination
The main aim of this research work is to study new approaches to assessing the results of forensic microscopic analysis of the investigated person's hair, which will improve the effectiveness of forensic biological examination of human hair. The forensic examination of human hair includes an analysis of their morphological characteristics. If all individualising features coincide, a conclusion can be drawn that this very hair probably belongs to the investigated person. However, a "probabilistic" conclusion cannot be the basis for a court decision. A mathematical model for assessing the probabilistic-statistical estimate of the set of matching features that characterise human hair (random match probability) has been developed to improve the evaluation of the forensic microscopic hair analysis. The identification significance (rarity) has been estimated for all morphological features characterising human hair. The aggregated identification significance of the set of matching features (morphological hair profile) has been estimated, and the probability and the frequency of morphological hair profiles have been evaluated for a control dataset of hair samples. As a result of the work, it can be concluded that, in most cases, the probabilistic-statistical estimate of appearance of morphological profiles of human hair does not give us precise data to make an unequivocal positive conclusion in the identification of a person by hair. However, the microscopic hair analysis is scientifically justified, and its results have a good correlation with the results of the DNA analysis, especially if the analysis made an unequivocal negative conclusion. The most accurate method of forensic hair analysis is the DNA analysis. However, despite the fact that the nuclear DNA analysis is more suitable for an identification of a person by hair than the microscopic hair analysis, it should be noted that, in two-thirds of cases, the probability of appearance of a genetic profile is in the same range of values as the probability of appearance of a morphological profile of human hair. Only in one-third of cases, this probability has values that are difficult to achieve in the microscopic hair analysis. Moreover, there are situations when it is impossible to perform the DNA analysis, but the microscopic analysis of human hair can be done without any restriction. As a result, it is concluded that, to increase the expert biologist's efficiency, it makes sense to use an integrated approach to the forensic examination of human hair. The integrated approach combines a consistent application of the method of the microscopic analysis of human hair and the method of the DNA hair analysis, which allows obtaining the most compete forensic information on human hair.