Human hair is a common type of physical evidence recovered at the scene of a crime or zones of mass disasters. It is traditionally subjected to light microscopy and nuclear DNA (nDNA) analysis. nDNA analysis is considered the most discriminating method, and can stand alone as a method for differentiation and identification of hair samples, given that the hair sample contains the root, and are therefore an un-degraded sample . The most commonly encountered hairs, however, are degraded samples. For degraded samples, microscopical and mitochondrial DNA (mtDNA) analyses are the most commonly used methods by hair examiners. However, these two analyses independently offer lower levels of discrimination than nDNA, as neither have the potential for individual identification in an open set population .
In their report entitled Strengthening Forensic Science in the United States: A Path Forward, the National Research Council of the National Academy of Sciences (NAS) stated that though microscopical hair analysis is a technique generally accepted in the scientific community, linking results of this analysis with a particular defendant is highly unreliable. In cases, where it seems that there is a morphological match, mtDNA analysis must be used to confirm in the absence of nuclear DNA. However, no studies have been performed to specifically quantify the reliability of their joint use and the high cost and time associated with mtDNA analysis has deterred many labs from using this method of analysis .
The NAS report highlighted the need to find a more objective method for hair examination that will add value to standard microscopical analysis, when nDNA and mtDNA analysis cannot be performed. The recent admission of decades of flawed hair analysis by the Federal Bureau of Investigation only supports the aforementioned need .
