A former Bay of Plenty Times journalist and author says there has only been serious suspect apart from Arthur Alan Thomas in the Crewe murder case - Jeannette Crewe's father Len Demler.
Chris Birt's comments come before the screening of documentary about the 42-year-old Crewe murder case on Television One tonight, in which Bryan Bruce will present his research on The Investigator: Who killed the Crewes?
Farmer Arthur Allan Thomas was convicted of the June 1970 killings at two trials, but was pardoned in 1979, leading to speculation that Len Demler was the prime suspect.
Mr Birt, who followed and wrote about the case in depth, has just released his book All the Commissioner's Men about the Harvey and Jeanette Crewe murders, a follow-up to his first book The Final Chapter which he spent 36 years researching and writing.
in it he focuses on what he says is a shocking chronicle of malpractice and suppression of crucial witness statements by detectives involved in the initial murder inquiry in their bid to resolve New Zealand's ultimate cold case.
"Thomas clearly didn't do it. If people believe there was a third person , who is the other suspect because everything I have assembled from the Crewe homicide file points clearly at Len Demler. Without seeing the documentary I can't comment on any speculation they may be producing tonight.
"From June 23, 1970, the day after Demler reported his daughter and son-in-law missing until October 2 that year when police conducted a conference to look at evidence against Demler, there was only ever one suspect and that was Len Demler.
"The Crewe homicide squad led by Detective Inspector Bruce Hutton went to great lengths to investigate peeping toms, persons with gazette notices, locals mentioned as possible killers, people with a grudge against the Crewes and those from the Pahiatua and Woodville area where Harvey Crewe had come from, and the Crewe inquiry squad was not able to gather evidence against anyone in these categories other than Demler.
"These conference notes and job sheets which I have gathered from the Crewe file over many years show this in very graphic detail.
"There only became someone else after October 2 when the police were unable to prove their case against Demler because they failed to put in his hands a firearm of a suitable calibre, and at that point they moved on to Arthur Allan Thomas," Mr Birt said.
Tonight's documentary is said to support Harvey and Jeannette Crewe's daughter Rochelle's belief that her grandfather Len Demler, who many suspected of being responsible for the murder of her parents, is innocent and nominates a third suspect who was not properly investigated.
Mr Bruce says the thrust of his documentary is that Len Demler didn't do it.
"And neither did Arthur Allan Thomas. There was a third person, a third option, that wasn't properly investigated, in my opinion," Mr Bruce said.