The color(s) of human hair--forensic hair analysis with SpectraCube

Human hair is among the most common kind of evidence secured at crime scenes. Although DNA analysis through STR-typing is possible in principle, it is not very promising for telogenic hair or single hairs. For the mixed traces frequently found in practice, composed of different hair from an unknown number of individuals, mtDNA sequencing of each individual hair seems to be the only possible, even if technically elaborate, solution. If it were possible to pool all hair belonging to an individual prior to DNA analysis, then this effort could not only be reduced, but the number of hair for an STR-approach could also be increased. Although it is possible to examine hair microscopically, this method must be considered unsuitable for pooling, since the results depend strongly on examiner experience, and the hair cannot always be correctly attributed to an individual. The goal of this study was to develop an objective non-DNA-contaminative pooling method for hair. To this end, the efficacy of spectral imaging as a method of obtaining information--beyond that obtained from a purely microscopic and morphological approach--for the identification of individuals was investigated. Three hairs each from 25 test persons (female: 18; male: 7) were examined with a SpectraCube-System and a light microscope. Six spectra were calculated for each hair, and the hairs from each individual were not only compared to each other, but also to those of the other individuals. From a forensic vantage, the examination showed, in particular, that individuals, whose hair could not be distinguished on the basis of morphology, could also not be accurately distinguished with the SpectraCube. The intra-individual differences were, in part, greater than the inter-individual differences. Altogether, the study shows that a person's hair color, as perceived, is composed of many naturally different, individual colors.