Bones found by the side of the M5 motorway in South Gloucestershire are those of a woman who has been missing since 1996.
A bin bag containing bones including a skull was found by a workman next to a slip-road at junction 14, on Monday.
Melanie Hall, 25, went out to Cadillacs nightclub in Bath on 9 June 1996 and has not been seen since.
Despite the offer of a £10,000 reward and several TV appeals, no trace of the hospital clerk had ever been found.
A workman stumbled across the bag as he was clearing vegetation on the slip road off the northbound M5, north of Bristol.
The discovery was said to include a significant number of bones, including a skull and pelvis.
Following examinations at a mortuary near Bristol on Wednesday, pathologists were able to confirm that the bones were from a female.
But sources at Avon Coroner's Office said cause of death was yet to be determined.
Det Insp Richard Budd said the death was being treated as "suspicious".
He added that only some of the bones were found in the bag - and others were scattered nearby and "partially buried".
Forensic teams set up a white tent at the scene shortly after midday on Monday, after the discovery at the exit for Thornbury in South Gloucestershire.
Miss Hall's next of kin have been informed.