Sandra Phillips' killer has not been found by the reinvestigation
Officers reinvestigating the 1985 murder of Sandra Phillips in Swansea say they have exhausted all lines of inquiry but not found her killer.
South Wales Police has apologised to the family for the shortcomings of the original investigation.
Ms Phillips, 37, was beaten and strangled at the sex shop she managed.
Neath brothers Wayne and Paul Darvell were wrongly convicted of the murder and spent seven years in prison before being released in 1992.
Mother-of-four Ms Phillips' body, which had been doused in petrol, was found inside the locked shop in Swansea city centre in June 1985.
South Wales Police reviewed the case in 2002, led by Albert Kirby, the former head of Merseyside CID who led the investigation into the death of toddler James Bulger.
A reinvestigation of the murder began in 2004 and an appeal on the BBC's Crimewatch programme led to new information about people who went to the shop on the day of the killing.
South Wales Police said it had now completed the recommendations made by Albert Kirby, a Queen's Police Medal holder, following his independent review of the case.
It said members of Sandra Phillips' family and an independent advisory group, which was set up during the original review to overlook the investigation, had been updated on all the lines of inquiry and forensic opportunities.
In a statement, the force said it "remained fully committed in attempting to bring those responsible for her murder to justice".
It added: "But sadly, despite those efforts, those responsible for her death have not been identified."
The mother-of-four's body was doused with petrol inside the shop
The statement said that since 1985 there had been "significant changes in the way serious criminal offences are investigated and reviewed by the force".
Detective Superintendent Paul Burke said: "It is important to stress an investigation is never completely closed and any new information which is received will be fully investigated and the inquiry will be revisited periodically.
"This news will obviously be upsetting for Sandra Phillips' family and come as a disappointment for the Swansea community.
"We would like to thank those people who responded to our previous appeals and thank the media for their continued support in this investigation."
Shortly after the killing, unemployed brothers Paul and Wayne Darvell, who had lived rough and in hostels in the area, were jailed for the murder.
In 1992, the appeal court ruled their convictions were "unsafe and unsatisfactory" after being told that that the brothers had a history of confessing to things they had not done and that a police notebook had been altered.
After their release, each was later awarded £80,000 in compensation for the time they had spent in prison.
In March 2005, Paul Darvell, 42, was found dead at his home in Neath in what police considered a non-suspicious death.