Pathologists have found that Melanie, who vanished aged 25, suffered a fractured skull and jaw before her remains were dumped in a bin liner on a sliproad of the M5 near Bristol.
The officer in charge of the murder hunt, Detective Superintendent Mike Courtiour, held a press conference close to the scene where he also displayed rope similar to that used to bind her in the black binliners in which she was found.
The two inch thick blue rope was found bound around the black bin bags which contained Miss Hall's remains and is still undergoing extensive forensic tests.
Mr Courtiour said the rope, which is commonly used and can be bought from hardware stores, could hold vital clues.
He appealed to the public to contact the police if they know anyone who has used a similar type of rope in the past.
He said: "Who had access to similar blue rope 13 years ago in their car, house or garage?
"There is someone out there who knows who killed Melanie and then bound her body here in this blue rope."
He added: "Showing the blue rope today may just prompt someone to remember.
"It is a widely available rope and we are well aware that people can pick it up from many DIY stores, but someone may know someone who bought it after Melanie's disappearance."
The Home Office pathologist who carried out the post-mortem examination on Miss Hall could not give a definitive cause of death but she had suffered severe blunt trauma to the head, causing a fractured skull, cheekbone and jaw.
Police are now preparing to comb or even excavate the surrounding area as part of the investigation and expect to be at the scene of the grim discovery for some time.
Melanie’s disappearance sparked one of the highest profile missing person’s cases of the 1990s. She had been last seen in Cadillacs nightspot in Bath on June 9 1996.
Her remains were discovered by a worman who was clearing vegetation at the site last week.
Her father, Steve Hall, a former chairman of Bath City Football Club, and Pat, held an emotion-charged press conference last week during which they told of their anger that their daughter’s remains had been “dumped like a sack of garbage.”
He urged the killer or his friends or associates, whom he believed was watching the appeal, to help the police.
Mr Hall, 65, said: “People out there know, they’ve lived with that secret for 13 years - now I’m appealing for the person who knows to come forward. Thirteen years ago we had a young vibrant daughter with a bright future in front of her. Today we have a bag of bones discarded here on the side of a motorway.”
He also described the killing as “horrendous” and added that the discovery, several years after Melanie had been declared dead, has caused “untold anguish” for his wife and family.
Mr Hall had added that they desperately wanted to know how she had met her fate.
There had been previously £10,000 rewards on TV appeals, including a reconstruction of the last time she was seen on Crimewatch. Despite the arrests of two men in 2003, nobody has been charged with thec rime.
Following the appeal, a man was arrested in connection with Melanie’s death in Manchester. However, he was later eliminated and is undergoing psychiatric tests.