Isotope analysis
A recent development in forensic science is the isotopic analysis of hair strands. Hair has a recognisable growth rate of 9-11mm per month or 15 cm per year. Human hair growth is primarily a function of diet, especially drinking water intake. The stable isotopic ratios of drinking water are a function of location, and the geology that the water percolates through. Sr, Sr and oxygen isotope variations are different all over the world. These differences in isotopic ratio are then biologically 'set' in our hair as it grows and it has therefore become possible to identify recent geographic histories by the analysis of hair strands. For example, it could be possible to identify whether a terrorist suspect had recently been to a particular location from hair analysis. This hair analysis is a non-invasive method which is becoming very popular in cases that DNA or other traditional means are bringing no answers.
Long hair
1972, it was estimated that 24% of American women wore shoulder length hair or longer (44% of women in ages 14 to 44), meaning slightly more than 12% of men and women altogether. Similar frequency was found in 2001, when it was estimated that about 13% of the US adult population, male as well as females, has hair shoulder-length or longer, about 2.4% have hair reaching to the bottom of the shoulder blades or longer, about 0.3% have hair waist length or longer, and only about 0.017% have hair buttocks-length or longer. By extrapolating the above data and the number of hair length records, the number of people with shoulder-length hair or longer in the USA is estimated to be 27 million, those with waist-length hair roughly 900,000, those with buttocks-length hair to be 40,000, with knee length hair to 2,000 and with ankle length hair to 70.