Hundreds of interviews and thousands of hours have failed to solve the mystery of who killed Auckland teenager Tracey Ann Patient.
The 13-year-old was last seen walking home from a friend's house in January 1976 and her strangled body was found the next morning in bush in west Auckland.
In January, police revealed they had re-opened the 40-year-old cold case in November 2015, saying they had new leads and were assigning eight detectives to work on it full-time.
Today, Detective Inspector John Sutton said they had wound down the investigation.
"The investigation has been progressed, but unfortunately it has not resulted in anyone being arrested and charged with Tracey's murder."
Over the last year, the investigation team had spoken to more than 200 people and detectives had travelled to Australia several times to carry out investigative work there, Mr Sutton said.
"Hundreds of theories and a number of leads have been explored across many thousands of hours."
A dedicated 0800 number had been inundated with calls.
"There have been hundreds of people who have contacted us to provide information from 40 years ago, people who had never been in touch before but had thought about the case since that time."
The number of people who had suggested names of those they thought might be involved was "quite astounding", Mr Sutton said.
Police had spoken to Tracey's family, he said.
"Whilst they share our disappointment, they are appreciative of our efforts.
"They have also been comforted at the ongoing public assistance with Tracey's case, and the fact that she has not been forgotten by hundreds of people in the west Auckland community."
The case would remain open but police would no longer actively investigate it unless they received new information, he said.
Many leads but no conclusion
January's announcement that the case had been re-opened was made with great fanfare, with police releasing an eight-minute video that included a new interview with Tracey's sister, Debbie.
Mr Sutton said at the time that, despite 40 years having passed, "someone out there knows who did this".
"As a result of new information that's come in over the last several months and a review of the file we identified there was new information that warrant us to launch a team to reinvestigate this."
A former detective who worked on the original investigation, Graham Bell, told RNZ in January the number of investigators involved signified a high level of interest.
"Eight detectives is a lot to assign to an old investigation so I'm very, very encouraged by that."
The original investigation in 1976 was also large-scale, with police looking at hundreds of persons of interest.
Twenty-two months after the murder, in November 1978, police received an anonymous phone call saying a signet ring Tracey owned was in a rubbish bin outside a chemist in Avondale.
The caller gave the calltaker the number "126040" and said he would call back later.
Officers went to the rubbish bin and found a ring inside, which is believed to have been the ring Tracey was wearing when she went missing and had been given to her by a boyfriend.
Police said they had continued to receive calls about the case over the years, including theories around the "126040" number and nominations of persons of interest.