SOMEONE, somewhere in Southampton, could be harbouring a dark secret that has been gnawing away at them for more than 20 years.

He or she wrote an anonymous letter to detectives investigating the death of a woman who had been strangled and dumped in a water-filled ditch.

A fingerprint on the second-class letter, which bore a Southampton postmark, separates the killer of Sandra Court from justice.

Now, with fresh publicity, police hope a desperately conscience-stricken killer or someone with vital information might finally contact them.

Dorset detectives mounted a full-scale murder investigation after teenagers on a Duke of Edinburgh award scheme made the horrifying discovery at the Avon Causeway, between Burn and Sopley, on May 3, 1986.

A post-mortem examination revealed she had been strangled, but with minimum force.

Her body was identified the following day as that of the 29-year-old Sandra Court, who had just finished her job as a section head in the transactions department of a major insurance company to take up a post as nanny to a family in Spain the following week.

She had celebrated her departure, first at an office party, and then at Steppes nightclub in Swithuns Road, Bournemouth.

She had been with her younger sister, Jennifer, but they left the club separately.

Sandra took a taxi from the club and was dropped off at her sisters home in Downton Close on the Muscliff Estate in Bournemouth at about 2.45am.

Her sister, unfortunately, was not at home. It was the last confirmed sighting of her, although police received a series of reported sightings of her near her parents home in Moordown.

Sandras body was found clothed, except for her shoes. She had been wearing a white blouse, wide black belt and black ski trousers.

Her handbag and jewellery were missing, though some of the items were found in the next few days. They included: ñ A necklace half a mile from where her body was found ñ Her jacket near Bransgore ñ A cosmetic bag in a New Forest car park ñ Her photo card near Stoney Cross.

ñ A shoe near Ringwood ñ Part of her chequebook at Picket Post.

A police spokesman told the Daily Echo: The motive for the murder is unclear. There is no evidence of sexual interference, nor were valuable items or large sums of money missing. She had no known enemies. The precise time and location of her death are still not known.

Police received some 2,000 calls from the public offering information. Eleven thousand five hundred inquiries had been investigated, more than 3,600 people had made 4,300 statements, 5,000 sets of fingerprints were taken, and almost 63,000 man-hours had been dedicated to solving the mystery.

However, following widespread publicity, the officer then leading the inquiry, Det Supt Alan Rose, received a poignant letter with the Southampton postmark on May 16.

The writing was plain, the words simple. It claimed Sandras death had not been deliberate.

It read: Dear sir, I amwriting to tell you that the tragic death of Sandra Court was a complete and utter accident, in no form is the person a killer or murderer. The person concerned is deeply unhappy, hurt and in total shock. The only reason the person has not come forward is the fact of being afraid that their explanation will not be believed. Please I beg take this letter to be of the truth.

The claim was later repeated in a telephone call to the BBCs Crimewatch programmeafter a TV reconstruction of her last movements.

Police have eliminated everyone who could have handled the cheque. They now believe the only person who could have handled it is the killer who tore it up.

Detectives interviewed John Cannan, who has been linked with the murder of estate agent Suzy Lamplugh, during the course of their inquiries.

Cannan, 53, is serving a life sentence for the kidnap and the murder of newlywed Shirley Banks, whose body was found in a water-filled ditch in Somerset. She had been hit over the head with a large stone.

Today officers from the countys major crime team are still hopeful the letter writer may yet come forward following further publicity about the case in the Daily Echo.

A spokesman said: We would like to hear from anyone with information about the murder or know who is responsible.

ñ Call Dorset police on 01202 22222 or Crimestoppers on 0800 555 111.