Hair and fibers and other trace evidence are often unknowingly left at the crime scene by the perpetrator. And those clever CSI folks can find these tidbits and analyze them. From hair, they can usually determine the species (human, cat, dog?), the color, the thickness and curliness, whether it was cut or yanked out, and other things.
But what if the hair has been altered with coloring or various chemical treatments? No problem. In fact, such alterations could add another layer of individuality to hair found at a crime scene. Using Surface-enhanced Raman Spectroscopy (SERS), dyes and chemical treatments can be analyzed and such analysis can lead to the type of treatment and even the manufacturer of the product. This could prove to be critical evidence in connecting a suspect to a crime scene.