For detectives in Newcastle, it had become the case they had to crack.
Ernest Wallace: Trapped by DNA evidence
An 11-year-old girl had been waiting for a bus when she was grabbed from behind and dragged into a park by a vicious rapist.
The assault in November 1981 had shocked residents in the city and police were under increasing pressure to catch the culprit.
After months of fruitless sifting through a morass of potential clues and leads, officers were forced to close down the major incident room and scale down the hunt.
But their sense of bitter frustration ended dramatically 23 years later after new DNA testing techniques were used in the biggest operation of its kind ever seen in Europe.
Operation Phoenix used genetic fingerprints garnered from scores of unsolved crimes to reopen cases which had gone "cold".
Forty one suspected sex offenders from the North East - at large for up to 26 years - have been identified using similar techniques since the investigation started in 2002.
And among the DNA profiles identified in the study was one belonging to Ernest John Wallace, who quickly became linked to the attack on the 11-year-old girl.
Det Insp Garry Dixon, of Northumbria Police, told BBC News Online: "The actual feeling within the community was running very high as it was an 11-year-old girl.
"I can't imagine how the victim would have felt, she had to live with this crime for the rest of her life and the trauma that at any time she could walk into this person.
"And as police officers you do not forget a case like this, you can carry one around with you for many years."
Wallace was convicted of the 1981 rape and a similar offence from 1977 - also as a result of information from Operation Phoenix. He admitted both offences at the city's crown court and on Tuesday was sentenced to 20 years, 15 of them in prison and five on extended licence.
By reviewing historic evidence, police chiefs have been able to secure 12 convictions, including three life sentences.
Mr Dixon said it is the most successful operation he has been involved in during his 26 year career.
"This is the largest commitment to cold case review in Europe," he said.
"Its success has been absolutely phenomenal, beyond anyone's expectations."
Partnership involving the police, the Forensic Science Service, the Crown Prosecution Service and Victim Support.
Crimes solved so far date back to 1977
Convictions range from serial rape to indecent assault
Sentences range from a double life sentence to a two year probation order
The operation aims to: Arrest and prosecute offenders
Identify new detection opportunities for unsolved crimes
Establish a force database of these offences
Identify possible links and behaviour patterns
Make a substantial contribution to the National DNA Database
The idea came from the Macpherson report into the murder of Stephen Lawrence, which recommended revisiting undetected major crimes.
Police in Northumbria responded by reviewing the evidence from all unsolved rapes and sexual assaults committed as far back as the mid-1980s to see if advances in science could help.
So far most of the reopened cases have relied on obtaining genetic profiles which were then fed into the national DNA database to check for matches.
Mr Dixon said most of the victims have supported the operation - only two have declined to have their cases reviewed.
"Victims of crime have come forward and have been absolutely amazed that we are showing interest after so long, they have been hugely grateful."
He said 41 DNA profiles, also retrieved through the investigation, have not yet been matched to anyone but will be retained on the national database for a possible future "hit".
"With changes in the law when any person is arrested they will be sampled and I am positive that will have an impact," he said.
"I am not saying it goes far enough but what we have got is better than anywhere else in the world.
"It is a dynamic sort of operation and is open to all sorts of scientific developments."
He added Operation Phoenix was now being used as an example to other forces across the country and had been presented to a conference in the United States.