Somewhere out there the killers of numerous New Zealanders are walking free, some for more than 30 years.
But while the leads have diminished and the files have gathered dust, police are determined to bring those killers to justice.
All cold case murder files remain open until they are solved. Most have senior detectives assigned to them, ready to investigate any new information that comes to light.
In February 1962, Dunedin lawyer James Ward died from injuries after opening a parcel bomb in the morning mail. Police have been unable to establish any motive for the murder, or make an arrest.
Welsh hitch-hiker Jennifer Mary Beard, 25, was strangled in a sexually motivated attack on New Year's Eve in 1969. Her body was found under the Haast River Bridge 19 days later.
A Christchurch police spokesman said the file remained open but there had been no new information provided to police for about 2 years.
Mona Blades, 18, disappeared while hitchhiking from Hamilton to Hastings on Queen's Birthday Weekend in 1975. She was last seen getting into an orange Datsun and her body and belongings have never been found. Police say she was murdered.
This week, Bay of Plenty police examined the concrete pad of a house in Kawerau after receiving information but found nothing.
In September 1983, Napier schoolgirl Kirsa Jensen disappeared while riding her horse Commodore. The 14-year-old was last seen by an old gun emplacement near the mouth of the Tutaekuri River.
Her horse was found tethered nearby, but Kirsa was never seen again. The officer in charge of the file, Detective Sergeant Bryan Schaab, once told the Herald that it was rare for new information to come to light after so long. But he was ever hopeful he could resolve the case.
Claire Hills' murder was described as one of the most callous in New Zealand history. The 30-year-old was abducted at traffic lights in Auckland in the early hours of April 28, 1998.
Her abductor took her to the top of Mangere Mountain , doused her in petrol and set her alight. "Operation Hills will be open until it is solved," said Detective Inspector David Lynch, who is now in charge of the file. "Police receive fresh information from time to time, that information is investigated by a team of detectives appropriately.
"For anyone who has information about what happened to Claire Hills that night - police urge them to come forward. It's only a matter of time. A prime example of this is the 1979 homicide that was resolved [a pensioner was arrested in Rotorua and charged with murder last month] - anything is possible."
In January 1998, the body of Ashburton teenager Kirsty Bentley was found in a paddock at the Rakaia Gorge, covered by branches. She had disappeared 18 days earlier and was killed by a blow to the back of the head with a heavy weapon. Police still get calls from the public about Kirsty's death 14 years later, and have several hundred "persons of interest".
Detective Superintendent Peter Read said yesterday that all new information received was assessed to see if it could take the case forward.
"Police and ESR do proactively review cases from time to time in terms of looking at the evidence that is held, and whether there are opportunities to re-test evidence in the light of ongoing advances in technology.
"We continue to ask anyone who has information on unsolved cases to come forward - we want to hear from them and we will follow through on any new information."
Victims whose murderers have gone unpunished
* Ashburton teenager Kirsty Bentley's body was found in the Rakaia Gorge 14 years ago. Claire Hills (left) and Kirsa Jensen, who was 14 when she went missing.
* James Ward was killed by a parcel bomb. Jennifer Beard died in 1969.
* Tracey Ann Patient was 13 when she was murdered while walking to her Henderson home in January 1976.