Killing of Rachel Nickell

Rachel Jane Nickell (23 November 1968 – 15 July 1992) was killed on Wimbledon Common in southwest London on the morning of 15 July 1992. She was walking her dog with her two-year-old son, Alexander, when she was stabbed 49 times in the neck and torso and sexually assaulted in a secluded part of the Common. Alexander was physically unharmed and was found clinging to his mother's body by a passer-by.

The Metropolitan Police investigation, conducted under heavy press and public pressure, questioned 32 men and focused on Colin Stagg, a local man known to walk his dog on the Common, despite the absence of forensic evidence linking him to the scene. Police enlisted criminal psychologist Paul Britton to produce an offender profile and to help design a covert operation, code-named Operation Edzell, in which an undercover policewoman feigned a romantic interest in Stagg over several months to try to elicit a confession or self-incriminating material. Stagg did not confess, explicitly denying involvement when prompted, but was nonetheless charged, based on claims he had described details of the crime scene said to be known only to the killer.

At the Old Bailey in September 1994, Mr Justice Ognall ruled that police had acted with "excessive zeal" and deceptive conduct "of the grossest kind," excluding the entrapment evidence. With no other evidence, the prosecution withdrew and Stagg was acquitted. Lead detective Keith Pedder was heavily criticised, continued to publicly assert Stagg's guilt in the years after, and later took early retirement; a subsequent corruption case against him was dismissed before trial for insufficient evidence.

The case went cold until pressure on anniversaries kept it under review. It was folded into Operation Enigma in the late 1990s, and a dedicated cold case team began collating evidence from 2000. In 2002, refined DNA techniques were applied, and by July 2003 a male DNA profile not matching Nickell's partner or son had been recovered from her clothing. Investigators reassessed similarities with the November 1993 murders of Samantha Bisset and her four-year-old daughter Jazmine in Plumstead — a link that Nickell-case detectives had earlier rejected with "hostility" when raised by the Bisset investigators. Robert Napper, convicted in 1995 of the Bisset murders and detained at Broadmoor Hospital with diagnoses of paranoid schizophrenia and Asperger syndrome, was interviewed by the cold case team in July 2006 and charged with Nickell's murder on 28 November 2007. He pleaded not guilty in January 2008, but on 18 December 2008, at the Old Bailey, pleaded guilty to Nickell's manslaughter on grounds of diminished responsibility. He was ordered detained indefinitely at Broadmoor.

An internal review put the cost of the wrongful pursuit of Stagg at roughly £3 million. Stagg received compensation of £706,000 for wrongful prosecution, confirmed in 2008, and a public apology from the Metropolitan Police in December 2008, as well as an apology from Napper via his QC. The undercover officer involved separately received an out-of-court settlement of £125,000 from the Metropolitan Police in 2001. A 2010 Independent Police Complaints Commission (IPCC) report described "a catalogue of bad decisions and errors," including the elimination of Napper from earlier rape inquiries due to a height discrepancy and the failure to act on a report from Napper's mother that he had confessed to a rape; the IPCC concluded these failures meant Napper was free to kill Nickell and, later, the Bissets.