EXCLUSIVE: Son of murdered Sheffield woman fears killer could strike again
Daniel Grainger, who was five years old when his mum, Patricia, was killed, said he wants the anniversary to be 'one final push for justice'.
The 25-year-old said he is devastated that the killer could still be walking the streets today - free to strike again.
Patricia was stabbed, sexually assaulted and strangled before her body was dumped under a bed base near a brook close to the family home in Parson Cross, in August 1997.
The mum-of-one, who lived in Buchanan Road at the time of her death, had learning difficulties and the mental age of a 10-year-old.
Nobody has ever been prosecuted.
Today, Daniel, who is a carer for his grandfather in Fox Hill, Sheffield, said he is desperate for justice for his mum.
"It would be some comfort to me knowing that whoever did this was dead because to think that they are still walking the streets sickens me," he said.
"I saw the autopsy results and what they did to my mum can only be described as sadistic. To think that somebody like that is still out there and free to attack again is an awful feeling.
"I wouldn't wish it on my worst enemy but I sometime think that they only way the police are going to catch who did this is if they actually did something similar again. It's awful to think that somebody else might have to suffer to solve my mum's case."
To mark the anniversary and encourage people with information to come forward, a mobile police station will be based in Parson Cross on Thursday.
Posters will also be displayed around the estate urging people to pass on information which could help crack the case.
Daniel said he has limited memories of his time with his mum.
"My memories of her are not happy ones unfortunately," he said.
"Because she had learning difficulties she was a target in the area and I remember people spitting at her, picking on her and hitting her. It's just what seemed to happen those days, there didn't seem to be any understanding for people who were different.
"I have vague memories of us colouring in the living room and her playing with me but mainly they are sad memories."
Daniel, who set up the Who Killed My Mum website, and has issued regular appeals for information urged people to help the police solve the mystery.
"I have done everything possible I can do and the police have followed up everything they have, so they need some new lines of enquiry now," he said.
He added: "Something small which may seem nothing to someone else could be all it takes to solve the case so please if anyone knows anything please come forward."
Anyone with information on the murder should call South Yorkshire Police on 101 or Crimestoppers on 0800 555111.