David Bain was convicted in 1995 of murdering his parents, Robin and Margaret, and siblings Laniet, Arawa and Stephen in their Dunedin home.
He was found not guilty in a retrial in June last year, after his defence team had argued that Robin Bain had shot the other four family members before turning the gun on himself, with the motive being his incestuous relationship with daughter Laniet.
In The Investigator Special: The Case Against Robin Bain, screened on TV One last night, documentary maker Bryan Bruce called into question some of the evidence given by defence witnesses.
The documentary singled out the testimony of the retrial defence's surprise witness Daryl Young for special attention, quoting two people who contradicted the photocopier salesman's evidence about his dealings with Robin Bain as principal of Taieri Beach School.
Bruce said Robin Bain had been in effect put on trial and vilified without the benefit of a proper legal defence.
He said there was no forensic evidence linking Robin Bain to any of the murdered family and his documentary showed the questionable chain of actions Robin would have had to have performed -- including shooting himself without leaving any of his bloody fingerprints on the bloody gun.
Valerie Boyd, Margaret Bain's sister, said today the documentary was "a start to restoring Robin's reputation".
"We never for one minute believed all the rubbish about him, so this is just a start," Mrs Boyd told Radio New Zealand.
"I think that we'd like it to be all over, but I'd also like the truth to be out there. I think it's time David talked actually."
It was "appalling" the way Robin and the family had been vilified, she said.
"I think there's something really wrong with the law when people can say anything they like about dead people with no accountability," Mrs Boyd said.
"I think the law regarding hearsay evidence needs to be reviewed. I think it's criminal how reputations are able to be ruined."
David Bain supporter Joe Karam said today the factual basis of the documentary was "so askew as to be farcical".
"It's just unmitigated rubbish," he told NZPA.
"About the only thing I agree with him is that the police should be called in quickly, and they should be knocking on his door for masquerading as a serious documentary maker."
It was "disgraceful" that TVNZ screened the documentary without Bruce seeking input from the defence team, Mr Karam said.
"They refused to approach us."
Bain's lawyers only learned the documentary was being made earlier this year after the court sent them copies of letters from Bruce asking for court documents, Mr Karam said.
When in May they received another letter from the court saying the documentary was almost finished, the defence team wrote to TVNZ and Bruce asking for the documentary to be postponed.
"How can you possibly do a balanced programme about the defence case without talking to the defence?"
The documentary did not follow the normal broadcasting standards of balance and fairness, Mr Karam said.
"Huge claims were made solely for the purpose, I would say, of increasing ratings and getting people to watch it."
It was too early to say whether a complaint would be laid with the Broadcasting Standards Authority.
David Bain's lawyer, Michael Reed QC, said the documentary had glossed over a lot of evidence about Robin's depression and his motive for killing the family.
"I am disgusted by the fact [Bruce] didn't spend one second in court, that he is challenging the jury and that he was disrespectful of the system and of the judge," he told the Otago Daily Times.
David Bain's legal team would today consider what action, if any, it would take.
Police said they would issue a statement today.
