A psychopath who butchered a Scots mother and her daughter 15 years ago admitted to the killing of Rachel Nickell.

The confession of serial sex attacker Robert Napper, 42, yesterday brought to a close one of the most infamous unsolved murder cases in recent legal history.

Following the conclusion of the trial at the Old Bailey in London, the Crown Office and Metropolitan Police issued public apologies to Colin Stagg, who was mistakenly targeted by police based on flawed psychological profiling.

They also said sorry to relatives of Miss Nickell and Scots-born Samantha Bissett and her four-year-old Jazmine, also killed by Napper, for missed opportunities to arrest the killer which could have saved their lives.

A senior officer admitted that Napper could have been arrested before the Wimbledon Common killing after his mother reported an earlier rape.

Rachel, a 23-year-old part-time model, was stabbed 49 times on Wimbledon Common on July 15, 1992.

Her two-year-old son Alex, who had watched his mother's killing, was found by a passer- by clinging to her blood-soaked body, crying "Wake up, mummy". A piece of paper had been placed on her forehead by Alex to form a plaster.

The boy was later given counselling and was eventually taken to live in France by his father in an attempt to give him a fresh start.

Napper was treated as a suspect after he admitted butchering 27-year-old Miss Bissett, originally from Dundee, and smothering her daughter in November 1993.

Napper, who has been in Broadmoor maximum security hospital since 1995, was finally charged in 2007 after a five-year, multimillion-pound reinvestigation by police.

The breakthrough came after microscopic traces of DNA taken from Miss Nickell's body, which would have been undetectable in 1992, matched his profile.

He denied murder, claiming diminished responsibility. Victor Temple, QC, prosecuting, yesterday confirmed that the plea was acceptable to the Crown. Mr Justice Griffith Williams ordered Napper's detention in Broadmoor under the Mental Health Act "without limit of time".

Rachel's parents Andrew and Monica Nickell kept their composure yesterday as they saw their daughter's killer finally brought to justice.

After the case, Assistant Commissioner John Yates said "mistakes were made" as Colin Stagg was targeted.

He said: "In August 1993 he was wrongly accused of Miss Nickell's murder. It is clear he is completely innocent of any involvement in this case and I today apologise to him for the mistakes that were made in the early 1990s."

Crown Prosecution Service lawyer Rene Barclay said outside court that he had written to Mr Stagg to express "regret" that the prosecution against him was brought.

Mr and Mrs Nickell continued to believe for many years that Mr Stagg was their daughter's killer and even considered taking civil action against him.

But Mr Nickell said yesterday: "It's easy with the benefit of hindsight to say mistakes were made. But we never felt at any time that the officers and staff involved in the investigation gave less than their very best."