In 1992, the TV news constantly ran footage of an attractive young woman dancing gaily across Wimbledon Common. It was Rachel Nickell, who had been brutally murdered in front of her two-year-old son. The police became convinced that she was killed by Colin Stagg, a loner who fitted the profile suggested by forensic psychologist Paul Britton. It took 16 years, a revolution in DNA technology and another, even more violent murder of a young mother before the real killer, Robert Napper, was convicted. Mark Austin pieces together the string of staggering mistakes and oversights by the investigation team that led to the wrongful conviction. What we will probably never know is whether it was mainly Britton's input or the police's determination to get a result that almost let Napper get away with it.

• Mark Austin