A 2009 testimony from Daryl Young was investigated by police after documentary film-maker Bryan Bruce challenged the evidence last year.
Bain was acquitted in 2009 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.
One News reported last night Mr Bruce received a letter from police - 10 months after he asked for an investigation, which concluded Mr Young gave false evidence at the retrial.
"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.
Police last night declined to comment.
Mr Young's lawyers said the letter "contains a completely gratuitous and totally unfounded allegation" and complaints had been laid with Police Commissioner Peter Marshall and the Independent Police Conduct Authority.
In March, TVNZ was ordered to pay Mr Young $1500 after the Broadcasting Standards Authority found the documentary breached a standard of fairness.
• Additional reporting by NZPA
