Robert Napper evaded suspicion for years after Rachel Nickell was killed on Wimbledon Common in July 1992, even though the investigation eventually showed police had already come close to him. While detectives pursued Colin Stagg through an undercover honey trap operation, Napper remained free and went on to attack again.

That matters now because the Nickell case still stands as one of Britain’s most disturbing failures of detection, and the details only sharpen the contrast between what police knew and what they chose to believe. Rachel Nickell, 23, was killed while her two-year-old son stood nearby, a detail that has never left the case and still defines its cruelty.

Napper, born in 1966, had already built a record of disturbing behaviour, stalking and sexual violence before he was linked to the killing. In the late 1980s and early 1990s he became known as the Green Chain Rapist after a string of violent sexual assaults near the Green Chain Walk in south-east London, but different police departments failed to properly share intelligence about him and the rape inquiries. That failure left a man with a violent pattern in the shadows while the Nickell investigation fixed on another suspect.

By August 1993, officers had interviewed Napper after complaints that he had been spying on a woman. Internal notes described him as strange and as someone who should be considered a potential sex offender, yet the case against Stagg still moved ahead. The gap between those two tracks — a man already raising concern inside police files, and another man targeted in a covert operation with no forensic evidence tying him to the crime — became the central flaw in the inquiry.

The cost of that mistake became clearer in November 1993, when Napper killed Samantha Bisset and her four-year-old daughter Jazmine in Plumstead. He was later diagnosed with paranoid schizophrenia and detained indefinitely at Broadmoor Hospital, but by then the damage to the Nickell case was already done. Colin Stagg was acquitted and the police operation against him collapsed publicly, leaving the original murder inquiry discredited and the real killer still not fully exposed.

Scotland Yard faced repeated pressure to reopen the case by the late 1990s, as criticism grew over how long Napper had stayed out of suspicion. Years later, advances in DNA technology finally brought the truth into view, showing that the question was never only who police chased, but how a dangerous offender could remain in plain sight while investigators looked elsewhere.