DNA traces were found on a piece of string wrapped in trash bags
containing the body of Melanie Hall, who was killed 23 years ago.
Police say it is "possible" that the DNA could belong to Hall's killer.
The 25-year-old from a Royal United Hospital office in Bath was last seen alive at the Cadillacs nightclub in the city at 1:10 am on June 9, 1996.
Police retrieved a 13-foot long 4mm rope. Pic: Avon and Somerset Police
Their remains were discovered 13 years later, on October 5, 2009, near junction 14 of the M5 north road by workers mowing.
Eleven arrests were made during the investigation into Hall's murder, but no one was charged.
Detective Chief Inspector James Riccio of the Avon and Somerset Police said police had previously revealed that DNA had been recovered from an item found by Hall's body.
Anyone who has seen Miss. Hall after 1:10 am on June 9 or saw her leaving the nightclub should contact the police. Pic: Avon and Somerset Police
"Today, we are confirming that the traces of DNA were found on a piece of blue polypropylene rope wrapped in thin black garbage bags that contained his body," he said.
"We retrieved a 13 meter long 4mm rope scene made up of four separate, intertwined lengths.
"In addition to the three knots that joined the ropes, there were four more on the string – a total of seven knots.
His clothes, jewelry and bags were never found. Pic: Avon and Somerset Police
"It is commercially manufactured rope and commonly used on construction sites and for pulling electrical cables through gutters."
When asked if the DNA traces could be those of Hall's killer, Riccio replied, "It's possible."
He described DNA as being "in its embryonic stages," but said advances in technology are being developed every day.
"We are confident that with corroborative evidence this will lead to an accusation," he said.
Police believe the area where Hall's remains were discovered is "fundamental."
Her body would have been left "hastily" in the undergrowth on the morning of June 9, 1996, or within a few days of that date, they say.
It is likely that the person entered the M5 motorway north and at the next intersection, or would have turned off Michaelwood services to return south.
"It's a rather weird place to dump a body," Riccio said.
"People know how Melanie got here. People know how Melanie died."
He said it is "highly likely" that the person who left Hall's body in the vegetation will be familiar with the area.
The person who did this may not have killed her, he said.
In a direct appeal, Riccio asked this person to report to the police on behalf of Hall's family.
"You have lived with a dark secret for years, but your guilt and fear are nothing compared to the lasting pain experienced by Melanie's family," he said.
"I want to make it clear – our main focus is to identify the person or people who killed Melanie."
In a statement, Hall's father Steve Hall said it was 23 years ago that his youngest daughter was murdered.
"Since then, Avon and Somerset police have invested numerous resources in trying to find the killer," Hall said.
Your silver earrings are also missing. Pic: Avon and Somerset Police
"Unfortunately, this goal has not yet been met, although my family and I remain eternally optimistic that eventually they will succeed.
"In our family we will always suffer and miss our lovely daughter. A young woman whose life stretched before her until that fateful night in June 1996, when that life was cruelly torn from her.
"She will never fulfill her life's ambitions, never get married, never have children, and my wife and I will never have another grandchild."
Police are asking anyone who has a piece of blue polypropylene rope that disappeared around June 1996 or who knows someone who has such a rope and whose behavior has changed since that date to perform.
They want to hear from the people involved in Hall's murder, including helping to leave his body in the undergrowth.
Anyone who has seen Miss. Hall after 1:10 am on June 9 or saw her leaving the nightclub should contact the police.
Detectives also want to hear from anyone who has seen suspicious activity or a vehicle parked at junction 14 of the M5 north road in Thornbury in the early hours of June 9 or days later.
Hall's pale blue silk dress, black suede shoes, cream jacket, and black purse were never found, plus cosmetics, his checkbook, and bank card.
Her jewelry, including a expanding watch with a bracelet and a pair of silver earrings, is also missing.
The scene where Melanie Hall's body was found
Anyone with information should call Operation Denmark incident room on 01278 648934 or provide information. connected.
A force spokesman said: "Melanie's parents have reinstated a £ 50,000 reward for information provided to the police, leading to the arrest and conviction of the person or persons responsible for Melanie's murder.
"The independent charity Crimestoppers is also reinstating a reward of up to £ 10,000 for information leading to the arrest and conviction of the person or persons responsible for the Melanie Hall murder.
"You will only qualify for this reward if the information is passed directly to Crimestoppers."
To date, Avon and Somerset Police have received 1,751 public calls about the case and made 1,668 statements.