Death on the Common: Channel 4 documentary about Rachel Nickell who was killed on Wimbledon Common in 1992

Alex Hanscombe, who was only a toddler when he watched his mother die, revisits her killing for new programme

Rachel Nickell was just 23 years old when she was stabbed to death while walking her dog on Wimbledon Common, in southwest London, with her toddler son.

On the morning of 15 July 1992, they were passing through an area of woodland when the young mother was knifed 49 times and sexually assaulted.

Her killer fled, leaving two-year-old Alex – the sole witness – alone with her body.

A passer-by found the child clinging to his mother’s body repeatedly asking her to get up.

Months later, Alex’s grieving father Andre Hanscombe moved him first to the south of France and then to Barcelona, in Spain, in a bid to start a new life.

In the desperate hunt to find Nickell’s killer, London’s Metropolitan Police quickly homed in on a man named Colin Stagg who was known to walk his dog on the Common.

Stagg had been there on the morning of the stabbing and had previously revealed a sexual fantasy that was reported to the police after Nickell’s death.

There was no forensic evidence linking Stagg to the scene of the attack, so investigators asked criminal psychologist Paul Britton to create a profile of the killer, later deciding the newspaper delivery man was their chief suspect.

Metropolitan Police handout custody photo of Robert Napper taken in 1992 (Metropolitan Police/PA)

In a bungled police investigation code-named Operation Ezdell, an undercover officer going by the pseudonym “Lizzie James” was brought in to see if she could elicit a confession from Stagg.

The policewoman wrote letters of a sexual nature to the suspect and they also met several times so she could gain his trust.

She managed to draw out fantasies from Stagg that Britton interpreted as “violent”, but Stagg did not admit to killing Nickell.

Stagg was charged with the murder but the trial against him later collapsed when a judge condemned the police for the “honey trap” undercover operation.

While investigators were focusing all their attention on the wrong man, the real murderer was left free to kill again.

Eighteen months after Nickell was killed, Robert Napper murdered 27-year-old Samantha Bissett and her four-year-old daughter Jazmine after forcing his way into their home in Plumstead, south London.

It was not until 2008, 16 years after the attack, Napper eventually admitted Nickell’s manslaughter on the grounds of diminished responsibility.

By this point, he had been a patient at Broadmoor Hospital for more than a decade suffering from paranoid schizophrenia and Asperger’s.

Stagg eventually received £700,000 compensation from the police and James medically retired in 1998 with post-traumatic stress disorder. She was also given £125,000 in compensation for psychiatric injury.

Alex will revisit his mother’s killing in documentaryDeath On The Common: My Mother’s Murder, which airs on Channel 4 at 10pm on Tuesday.