The Weekend Herald has spoken to several sources with knowledge of the case who believe the accused, a former Taupo real estate agent, told his wife at the time what happened.
Taupo Mayor Rick Cooper said he was pleased an arrest had been made after so long and congratulated the police.
He knew detectives involved in the original inquiry into Mr Tahu's murder.
"I know the evidence of the wife, girlfriend or partner couldn't be used."
Mr Tahu's former boss, Roger Bryant, said: "We were told by the police that [a suspect] did tell his wife about it and they couldn't use the evidence."
At a press conference after the accused's Monday court appearance, Detective Inspector Mark Loper said the file on Mr Tahu's death had been reviewed regularly since 1979.
He said there had also been advances in technology and, crucially, changes to the laws of evidence.
Mr Loper would not elaborate on the changes, but the Evidence Act 2006 altered rules about a spouse giving evidence in criminal proceedings.
Under the old law, the Crown could not compel a spouse to give evidence without the consent of the husband or wife charged.
The law gave further protection to spouses in any court proceedings by protecting disclosures made duringa marriage by one spouse to the other.
But the law change in 2006 removed what was called spousal immunity.
Mr Bryant said he wanted closure for his friend, whom he often thought of despite the passing years.
"He was a very loyal worker, honest, and a very good family man. You couldn't have wished for a better person."
Mr Tahu had been working for him for four years when Mr Bryant installed computerised pumps.
But the new pump setup was complicated and staff knew only how to close the pumps down - not how to start them up.
"I wasn't wanting to confuse Rodney with everything else he needed to do, but unfortunately this guy came in and demanded fuel."
He believes Mr Tahu had just finished his shift, had locked the station up and was about to go home when the incident happened around 12.30am.
A passing truckie is understood to have found Mr Tahu's body lying in a pool of blood.
He was taken to Taumarunui Hospital, where he died of gunshot wounds to his head and shoulder.
Former local constable Don Ormsby remembers telling Mr Tahu to "give the buggers the lot" in the case of an armed hold-up.
The retired 67-year-old said he got a phone call around 5am on August 16, 1979, from his sergeant.
"He said, 'We've had a shooting that's turned into a murder'.
"I said, 'It's not Rodney Tahu, is it?"'
Mr Ormsby said it had been highly frustrating for the police that no one was charged with the murder.
"Rodney Tahu was a bloody good man, and he shot him in cold blood."
