A 45-year-old man arrested on suspicion of the murder of 25-year-old Melanie Hall has been released on bail.
The man, who has not been identified, was held on Thursday in connection with the death of the university graduate.
Miss Hall was last seen at the former Cadillacs nightclub in Walcot Street, Bath, in the early hours of June 9, 1996.
Her remains were found in vegetation off the northbound slipway at junction 14 of the M5 at Thornbury in 2009.
An Avon and Somerset Police spokesman said: "A 45-year-old man who was arrested as part of our investigation into the murder of 25-year-old Melanie Hall has been released on police bail, pending further inquiries.
"The man was arrested on Thursday in connection with the murder of Melanie in 1996. Melanie's parents continue to be supported by specialist family liaison officers.
"The man was released overnight."
Avon and Somerset Police now have DNA evidence from an item found at the scene where Miss Hall's remains were discovered.
On the 20th anniversary of her disappearance earlier this month, her parents Steve and Pat made an appeal for information and offered £50,000 of their own money as a reward.
Mr Hall said then: "We believe we're in touching distance of a significant breakthrough and feel it's the right time to offer a substantial reward to encourage someone to come forward with information.
"Someone may have been wavering over whether to provide information for a long time. This amount of money is life-changing and I hope it will provide the incentive for them to do the right thing.
"The loss of Melanie has been life changing for us and we'll never be the same people as we were before Melanie disappeared.
"Melanie's murder has had a terrible impact on our family and I know my wife Pat is tortured by what happened to our daughter, and will never get over it.
"I believe this inquiry will be solved by one of two things - either through the advancement of DNA helping to identify who was responsible, or someone who knows a crucial piece of information having the moral fibre to contact the police.
"I hope by us offering this reward, it'll encourage this person or these people to come forward."
The force does not have a prime suspect or any conclusive evidence that Miss Hall's death is linked to other murders or sexual offences.
Police have previously arrested nine people in connection with the case since the investigation began but no-one has been charged.