On Merseyside the police are congratulating themselves on a job well done. The investigation into the murder of Rhys Jones was one of that force’s most difficult cases, but detectives secured the evidence and convictions that they needed.

In London the Metropolitan Police are reeling from having to make two public apologies in a week for disastrous operations.

Behind the contrast lie questions about the size of the two forces, their leadership and discipline. But the most important issue is the passage of time.

More than 16 years have passed since Rachel Nickell was killed as she walked on Wimbledon Common with her son and the family dog. Much has changed since then in the way that homicides are investigated, and it was the fallout from the Nickell case, and the ill-conceived pursuit of Colin Stagg, that drove those changes.

It was not quite Life on Mars, but the Nickell inquiry was run by former Flying Squad officers who knew more about big robberies than murders.

Today’s murder detectives are a more professional cadre. In London, a dedicated command investigates all murders and linked sex offences that might throw up a serial killer.

In the early 1990s, offender profiling was considered cutting edge. That is no longer the case. Detectives still use the services of forensic psychologists, but not on word-of-mouth recommendations from old mates. There is a national list of what are now called “behavioural investigative advisers” and their input is strictly of intelligence, rather than evidential, worth. They no longer shape or direct the course of investigations.

Perhaps the most important change since 1992 has been the advance in DNA testing technology. Then, forensic scientists could achieve a profile only from a body fluid stain the size of a 50p piece.

The material that provided the 1 in 12 million DNA match that proved that Robert Napper was Rachel Nickell’s killer amounted to nothing more than a few cells on a piece of adhesive tape.

Amid all the criticism, something should also be said for the persistence of the British copper. Despite the cockups and the embarrassment, the Met did not give up on finding Ms Nickell’s killer. of criminal justice. What is novel (or certainly extremely rare) is the emergence of conclusive proof that Mr Stagg was not exonerated on what has been repeatedly characterised as a “technicality”, but on the uncontestable foundation of truth and innocence.

I conclude with two personal reflections. First and foremost, I profoundly hope that the final disposal of this case will help to bring a kind of closure to those who loved and cherished the vivacious young woman who was Rachel Nickell, and who have been denied justice for so many years. And I hope that I can now be confident that the vendetta pursued against me by certain newspapers in the aftermath of the trial in 1994 is now put to rest.

It is too much to expect an apology: arrogance is rarely supplanted by decency. But at least this week – and long into my retirement - I can now look back on R v Colin Stagg as “emotion recollected in tranquillity”. With that, I am more than content.

The key players

Paul Britton
The forensic psychologist who advised on the operation to secure Colin Stagg’s conviction. He also worked on the Bissett murder but said in a book that the two killings could not have been by the same man. He is no longer on the police list of approved profilers

Keith Pedder
The detective inspector who led the investigation. He left the Met in 1996 and was charged with corruption in 1998 for allegedly trying to get information from police computer. The case was thrown out. He is recuperating from serious illness

Lizzie James
Pseudonym of the officer who tried in a series of explicit letters to get Mr Stagg to confess. She was awarded £125,000 for stress in 2001. She lives abroad and cannot be identified

Ian Johnston
The most senior officer in the case became an assistantcommissioner and is now in charge of British Transport Police. He conducted a review of the Met inquiry into Damian Green, MP

Dame Barbara Mills
The Director of Public Prosecutions when the cases against Mr Stagg and Napper were being pursued. She is now the Adjudicator, handling tax complaints

Mr Justice Ognall
He rejected the case against Mr Stagg. He has now retired but is a judicial member of the Proscribed Organisations Appeal Committee

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