THIS is the heartbreaking moment Rachel Nickell’s three-year-old son talked about his mum’s murder after she was stabbed in front of him.

Alex Hanscombe was just two years old when Rachel, 23, was stabbed 49 times and sexually assaulted as they walked on Wimbledon Common in 1992.

A horrified passer-by later found Alex clinging to his slain mother’s blood-soaked body crying “wake up mummy”.

Alex can now be seen in heartbreaking home video speaking to his dad André Hanscombe about what he saw.

The clip, which features in a new Netflix documentary, shows the youngster wearing a Thunderbird outfit as he opens up.

Dad André asks him: “Alex, look at me. When you saw the bad man, was he in front of me like I am, or was he on this side, or was he on that side?”

The youngster tells him the man was “in front of me”, prompting André to ask: “Did mummy see him?”

Alex says he does not think Rachel did see him before revealing the man had a bag.

André asked if he opened up or it if it was open already before Alex responds: “He opened it.”

When asked what he got out the bag, the toddler says: “A knife.”

André then asks his son “What did he do to you?” as Alex can be heard saying: “He knocked me over.”

The youngster then draws a picture on paper before his dad asks: “What’s he sticking in her?”

Alex says: “A knife, there’s his knife.”

When the dad asks him whether he saw the murder, Alex replies: “Yeah, I saw the knife.”

He continues: “I saw it, yeah I saw it all.”

Former model Rachel was settling into life as a full-time mum when she was brutally murdered by a complete stranger in a depraved crime that horrified the nation.

Serial sex offender Robert Napper had lurched from bushes and attacked her in a frenzied knife attack.

Rachel’s throat was slit, with cuts on her hands showing she had put up a fight.

Tragically, little Alex had stuck a piece of paper on Rachel like a plaster “to make mummy better”.

A huge police investigation was launched and 14 men were arrested in connection with her murder but all of them were released.

As the probe turned out more dead ends, officers put pressure on Alex to provide the smoking gun that could catch his mum’s killer.

This demand on the traumatised toddler caused dad André to move them both to the South of France and later Barcelona.

The police investigation continued in the UK after the father and son moved abroad and on September 21, 1992, cops targeted Colin Stagg.

The 29-year-old newspaper delivery man had been fined £200 after he pleaded guilty to indecent exposure on Wimbledon Common.

No forensic evidence linked Stagg to the scene but cops asked criminal psychologist Paul Britton to create an offender profile of the killer and decided he was their prime suspect.

A year later in August 1993, Stagg was charged with Rachel’s murder and stood trial a year later at the Old Bailey.

Stagg refused to eat for six days during this time.

Just months later, the trial collapsed after the judge condemned a police undercover operation in which a female officer exchanged a series of letters with Stagg.

Operation Ezdell – later branded a “honey trap” by Mr Justice Ognall – gave a female undercover officer the pseudonym Lizzie James.

Lizzie contacted Stagg and over five months wrote more than 40 letters, each more explicit than the last.

By the end, Lizzie was virtually demanding Stagg confess to Rachel’s murder in return for sadomasochistic sex.

But even faced with the opportunity to confess to the murder in return for the sex he so desperately craved, Stagg insisted he had nothing to do with Rachel dying.

The prosecution withdrew its case and Stagg was formally acquitted in September 1994 and later given more than £700,000 in compensation.

Alex said at the time: “It’s very unfortunate what happened to Stagg. It was one of a chain of errors made by the police, focusing on him and missing opportunities to apprehend the real killer.”

It was not until 2008, 16 years after the attack, that Robert Napper, then 41, admitted stabbing Rachel.

Napper had been a patient at Broadmoor Hospital for more than ten years suffering from paranoid schizophrenia and Asperger’s.

He had been convicted of killing Samantha Bisset and her four-year-old daughter Jazmine in November 1993 – 16 months after Rachel was slain.

Advances in DNA profiling meant police were able to link Napper to the murder in 2004.

He was convicted of her manslaughter on the grounds of diminished responsibility.

Police had missed a series of chances to arrest Napper before his six-year spree of sex and rape attacks was brought to an end.

The new Netflix documentary will explore Rachel’s killing using archive footage, first-hand accounts from family members. and insights from leading forensic experts.

The Witness will be available to stream on June 4, along with a three-part drama series based on the murder.