Gangs or associates of gangs are new suspects in the historic Mona Blades case following startling new revelations in a television documentary.

The Cold Case documentary, which screened on television last night has found the police investigation into the 1975 disappearance of Blades could have gone down the wrong track.

The documentary follows a small team of police who take another look at the famous unsolved disappearance of Blades, who vanished while hitch-hiking from Hamilton to Hastings at Queen's Birthday weekend 43 years ago.

Detective Inspector Mark Loper from Rotorua led the team of police which found officers working on the case possibly put too much weight on a truck driver's evidence that he saw Blades get into an orange Datsun on the Napier-Taupo Rd with a man.

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Her disappearance sparked one of the country's largest manhunts with more than 500 suspects who either owned or had driven orange Datsuns investigated.

However, not one piece of evidence or her body was ever found.

Her disappearance sparked one of the country's largest manhunts with more than 500 suspects who either owned or had driven orange Datsuns investigated. Photo/File
Her disappearance sparked one of the country's largest manhunts with more than 500 suspects who either owned or had driven orange Datsuns investigated. Photo/File

The documentary revealed the truck driver's evidence changed slightly each time he was interviewed by police, meaning he was possibly influenced by what he had heard and read of the case.

That meant the inquiry team possibly didn't put enough weight on other apparent sightings of Blades in the Taupo area, particularly from those who said they saw her drinking at the Spa Hotel in Taupo with another young woman.

Loper said in the documentary he now did not think Blades left Taupo alive.

The documentary revealed the public's perception of Blades was different to reality. Blades' family had provided police with photographs of her, which in hindsight weren't a true reflection of how she looked now.

The documentary revealed the photographs were from when Blades was a bridesmaid and her hair was long and curled when in fact when she went missing her hair was shorter in a mullet-style haircut.

It was said one of the witnesses who had earlier given Blades a lift initially thought Blades was a young man because of her haircut.

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Detectives on the Cold Case documentary said they discovered Blades had some affiliations with bike gangs in Auckland and Hamilton and it was possible that those gangs were on the road travelling to Wellington for a gathering over that long weekend.

The documentary revealed there were also sightings of a red Toyota station wagon that could have been travelling with a bike gang that corroborated with another witness who saw two people carrying a rolled up piece of carpet into the back of a red Toyota station wagon in Taupo.

Stewart Guy, a former police officer who worked on the case, was brought into Cold Case's new investigation team to offer some insight into the direction of the investigation at the time.

Guy said in the documentary police were trained at the time to ask for detail from witnesses, which meant interrupting them during their statements to ask questions. New techniques used by police today discourage officers from interrupting potential witnesses as research had shown it potentially impacted their memories.

It was made clear in the documentary that the truck driver wasn't suspected of deliberately making false statements.

Given the new information, the documentary called on members of the public to call police if they had any memories of the event which they might have thought was not significant at the time.

Loper told the Rotorua Daily Post today the police would be collating feedback from the public since Sunday night's screening.

He said the police were not prepared to name any particular gang or associates from Auckland or Hamilton who were now being looked at.

"I think the most important thing is we are keeping an open mind. We explored a number of areas during the inquiry. We are not going to release name of any particular group but it might well be we look at associates of a group and not those involved in a group themselves."

Three other mysteries will feature in the Cold Case series on TV One. The next is this Sunday at 8.30pm on the disappearance of Do Trieu from 2008. This will be followed by the cases of Kayo Matsuzawa from 1998 and Tuitania Barclay from 2002.