Under intense pressure to catch Rachel Nickell's killer, detectives resorted to unconventional tactics.
Colin Stagg, a loner who lived near Wimbledon Common, was identified as a possible suspect but police had no firm evidence.
So they set about ensnaring the young man using a so-called "honey-trap" - in this case a young policewoman who went undercover, befriending Stagg and enticing him into discussing violent sexual fantasies.
The officer, who used the alias Lizzie James, was brought in from Scotland Yard's covert operations unit SO10.
During a "friendship" lasting many months, Mr Stagg told Lizzie he had fantasised about Miss Nickell's killing but he never admitted responsibility.
Stagg was charged with the murder and held in custody for a year.
But the case was thrown out at the Old Bailey in 1994 by Mr Justice Ognall, who refused to put the undercover officer's evidence before a jury.
The judge said the use of the honey-trap tactic was "not merely an excess of zeal, but a blatant attempt to incriminate a suspect by positive and deceptive conduct of the grossest kind".
The undercover detective, who was not criticised for her role, found the experience so stressful that she was off work for 18 months and later took early retirement.
She said the pressure of working on the case caused her to suffer post-traumatic stress disorder.
She also accused Scotland Yard of failing to give her the necessary support and issued a writ against her employers in March 1999.
She was reportedly awarded £125,000 compensation.
The use of criminal profiling in the investigation also proved controversial.
Criminal profiler Dr Paul Britton, who was the inspiration for the TV character Cracker, was drafted in to help detectives.
Dr Britton, who was also involved in the Fred West and James Bulger murder inquiries, concluded that Mr Stagg had the same "sexually deviant-based personality disorder" as Miss Nickell's killer.
But he has always denied being responsible for the mistakes which led to the case being thrown out.
He later faced a British Psychological Society professional misconduct hearing but the case against him was dismissed after the disciplinary committee concluded his work on the inquiry could not be properly investigated.
Police say they are confident they have learnt from their mistakes.
Commander Simon Foy said: "We used Dr Britton to advise on the investigation. In retrospect and in hindsight, it was inappropriate for us to allow such a sensitive operation to be led in this way."
The hunt for Miss Nickell's killer became one of Britain's biggest murder inquiries, costing an estimated £3m.
Some 4,563 statements were taken and more than 6,000 male suspects considered for elimination.
Although 34 suspects were arrested, only Mr Stagg was charged with murder.
Following Robert Napper's sentencing for the sexually-motivated murders of Samantha Bissett, 27, and her four-year-old daughter Jazmine, he was interviewed by Nickell detectives in Broadmoor.
Napper was finally linked to the Nickell killing after a new police review was launched in 2001.
All the exhibits were re-examined using new DNA techniques which could produce findings from a minute particle.
But the Home Office Forensic Science Services lab used by police failed to find a positive reading.
The commercial Forensic Alliance lab (now the LCG) was brought in a year later.
Using advanced techniques, minute examination of Miss Nickell's clothes and other evidence was started.
After a profile was found for Napper, a new murder inquiry was launched.
Napper was interviewed again in 2006 and charged in 2007.
Mr Foy said: "He denied ever going to Wimbledon Common and stated that he would only admit his involvement in any offence for which police had forensic or supporting evidence.
"As his pattern of offending was specific to south east London, there was no evidence to link him to Wimbledon Common or the murder."
Mr Foy said the Homicide Command which he leads today was "significantly different".
He said: "We now have a unified command to ensure that intelligence and investigative opportunities are not missed."