A passer-by found him clinging to his mother's blood-soaked body, repeating the words "Wake up, Mummy", with a piece of paper stuck to her forehead as a bandage.
[citation needed] Officers of the Metropolitan Police undertook the investigation, under pressure to find the perpetrator by press coverage and public outrage at the circumstances of the murder.
[citation needed] Thirty-two men were questioned in connection with the killing; the investigation quickly targeted Colin Stagg, a man from Roehampton who was known to walk his dog on the Common.
As there was no forensic evidence linking him to the scene, the police asked Paul Britton, a criminal psychologist, to create an offender profile of the killer.
Over five months, she attempted to obtain information from him by feigning a romantic interest, meeting him, speaking to him on the telephone and exchanging letters containing sexual fantasies.
[5] The undercover officer won Stagg's confidence and drew out fantasies from him that psychologist Paul Britton interpreted as "violent", but he did not admit to the killing.
When the case reached the Old Bailey in September 1994, Mr Justice Ognall ruled that the police had shown "excessive zeal" and had tried to incriminate Stagg by "deceptive conduct of the grossest kind".
[13] In 2002, ten years after the killing, Scotland Yard used a cold case review team, which used refined DNA techniques only recently made available.
A small team of officers and retired veteran investigators analysed statements from witnesses, reassessed files on a number of potential suspects and examined the possibility that the case was linked to other crimes.
[14] In July 2003, reports surfaced that, after 18 months of tests on Nickell's clothes, police had found a male DNA sample which did not match her boyfriend or son.
(with novelist David Kessler) and, more recently, Pariah (with journalist Ted Hynds), the latter being published on the same day as the real culprit's appearance in court to enter a plea.
[27] The payout was widely criticised by various sources, particularly as Nickell's son had been granted £22,000 (less than a fifth of the amount paid to the undercover detective) from the Criminal Injuries Compensation Authority.
[28] The criminal psychologist involved with the investigation was charged with professional misconduct by the British Psychological Society, but in 2002, in lieu of any substantive hearings, further action was dismissed due to the time delay in bringing proceedings.
It said that officers missed a series of opportunities to take him off the streets and suggested the lives of Samantha Bisset and her four-year-old daughter, Jazmine, would also have been saved if police had acted on tip-offs, including one by Napper's mother.
Rachel Cerfontyne of the IPCC said that police failed to investigate the 1989 report that he attacked a woman on Plumstead Common in London and no record of the telephone call can be found.
She said, "It is clear that throughout the investigations into the 'Green Chain' rapes and Rachel Nickell's death there was a catalogue of bad decisions and errors made by the Metropolitan Police.
Without these errors, Robert Napper could have been off the streets before he killed Rachel Nickell and the Bissets, and before numerous women suffered violent sexual attacks at his hands".