IP reveals that hair has become one of the most common types of trace evidence. It says hair can help rule out certain populations or help identify an unknown victim. The transfer of hair from a victim to a suspect can raise the probability that the victim and perpetrator came in contact.
But IP points out that hair is never used as definitive proof to indicate guilt because visual comparison is subjective. But when hair is used with DNA, it adds, it becomes a powerful tool for an investigator. Today, hair analysis is only done when DNA tests can also be done.
Still, IP cautions that results from hair analysis can be controversial. The factors that affect these results include where on the body the hair was removed, the person's age and race, and even the color. Because standards vary, a single lab can report different results from the same hair sample and false-positives for illegal drugs are not uncommon.
Similar ambiguities regularly occur in the analysis of other crime-scene materials, including fingerprints and teeth.
Experts in fingerprint analysis will tell you no two fingerprints have ever been found identical in many billions of human and automated computer comparisons. Yet there have been errors. This is an oft-repeated art of thje forensics mythology.