A police investigation has found a photocopier salesman gave ''untruthful evidence'' at David Bain's murder retrial.
Daryl Young's 2009 testimony was investigated by police after documentary film maker Bryan Bruce challenged the evidence.
Bain was that year acquitted of murdering his parents, Robin and Margaret, and siblings Laniet, Arawa and Stephen in their Dunedin home.
Mr Young was a late witness in Bain's defence and told the court of his dealings with Robin Bain.
''I smelled alcohol and that's why I thought he wasn't at school,'' he said.
Ten months after Mr Bruce asked police to investigate, he received a letter saying Mr Young had given false evidence, One News reported tonight.
''I have concluded that untruthful evidence was given by Young. The investigation was referred for legal advice as to whether there was sufficient evidence to support a prosecution for perjury. It was determined that no criminal charges would follow,'' the letter from Detective Senior Sergeant David Harvey said.
Mr Young's lawyers said the letter ''contains a completely gratuitous and totally unfounded allegation'' and they had complained to Police Commissioner Peter Marshall and the Independent Police Conduct Authority.
Police could not be reached for comment.