'Twenty years of heartbreak'

They have also issued descriptions of three potential witnesses they hope hold the key to finally solving the murder of Sandra Phillips, who was 38.

She was beaten, strangled and possibly sexually assaulted in June 1985 at the Private Shop, which she managed.

Brothers Paul and Wayne Darvell were wrongly convicted of the murder of the mother-of-four and set free in 1992.

South Wales Police said they would use the 20th anniversary of the murder on Tuesday to re-examine the crime scene at Dillwyn Street.

I don't think whoever committed this crime has kept it a secret - I think that person would have unburden themselves Det Supt Simon Clarke

They said they would also use 3D imaging techniques used in the investigation of the murders of Holly Wells and Jessica Chapman in Soham to create a reconstruction of the shop as it would have looked in 1985.

A mobile police incident unit has been set up opposite the shop.

Detective Superintendent Simon Clarke has met the families of both Mrs Phillips and the Darvell brothers and pledged police would catch the killer.

"It's been 20 years of heartache and I made a commitment to them that I will resolve this matter," he said.

Mrs Phillips' body was found by the store's area manager at 1345 BST on 14 June 1985 although Det Supt Clarke said the time of the murder was around 1100 BST.

SHOP VISITORS Aged 25-26 in 1985, 5ft 10 ins tall, athletic build, dark brown curly hair, fringe over ears Age late 50s-early 60s, heavy build, neat short grey hair, dark clothing

One person recently came forward with fresh information and police now needed to speak to customers and visitors to the shop on the morning of the murder.

In particular detectives wanted to speak to three people who had never been traced.

The first was a man in his 20s, who was seen talking to Mrs Phillips in the doorway of the shop, the last reported sighting of her alive.

POLICE HUNT MAN WITH HAT Aged 35-40 in 1985 5ft tall, portly Smartly-dressed, with trilby hat Carrying a brown parcel under arm

Another man in his late 50s or early 60s was seen leaving the shop by another witness and locking it from the outside.

Detectives also want to speak to a short, portly man, with a trilby-style hat - similar to one the police produced at Monday's press conference.

When he left the shop and is believed to be the last customer the victim served.

Det Supt Clarke also said he was convinced that the killer would have told someone about what he had done and he appealed to them for help.

"I don't think whoever committed this crime has kept it a secret - I think that person would have unburden themselves."