Ms Doleac calculates that if every state kept the profiles of people arrested but not convicted, the US would see a fall of 3.2% in murders, 6.6% in rapes and 5.4% in vehicle thefts.

BBC: DNA and individual freedom v crime prevention

Last month Jennifer Doleac, assistant professor of public policy and economics at the University of Virginia, published a paper entitled The Effects of DNA Databases on Crime, which suggested that size matters: "larger DNA databases reduce crime rates".

BBC: DNA and individual freedom v crime prevention