Channel 4 will tonight (Tuesday) air a documentary about a mother who was murdered on Wimbledon Common in 1992.

Alex Hanscombe was only a toddler when he watched his 23-year-old mother Rachel Nickell die.

The pair were passing through a secluded area of Wimbledon Common when Nickell was attacked.

She was repeatedly stabbed and slashed with a knife before being sexually assaulted.

Two-year-old Alex was the only witness and a passer-by found Alex clinging to his mother's body repeating the words "Wake up, Mummy".

A lengthy police investigation to find the perpetrator followed, and 32 men were questioned in connection with the killing.

A suspect was wrongfully charged and later acquitted – before the case went cold.

In 2002, with more advanced forensic techniques, the case was reopened and on December 18, 2008 Napper pleaded guilty to Nick ell's manslaughter on the grounds of diminished responsibility.

Napper, who was already detained at Broadmoor High Security Hospital in Berkshire for a 1993 double murder, was ordered to be detained there indefinitely with the judge adding that it was unlikely he will ever be released.

Almost 30 years later, Alex's revisits his mum's killing in a documentary set to air on Channel 4.

Death on the Common: My Mother's Murder will be on TV screens at 10pm tonight (September 7).