"It demonstrates there has been talk between people about who's responsible."
Advances in forensic science also meant there was an increased chance of finding the killers, according to police.
The programme ended with a plea for anyone with information on the murder to come forward to police.
Bush was enjoying a drink with three other staff members just before midnight after closing up the tavern when two men burst in.
The two heavily disguised men, one carrying a double-barrelled shotgun and the other a baseball bat, stormed into the bar yelling "This is a hold-up".
As Chris stood up, he was shot and killed. One of the men then ordered a female staff member to search Chris' pockets for the key to the safe.
The offenders took off with $25,000.
"The men involved may have been intimidating 30 years ago, but they will now be middle aged or older and you may now feel comfortable contacting police. If you do know something, your calls will be treated in confidence," Lendrum said.
Anyone with information that could assist the investigation is asked to contact Counties Manukau Police on 09 263 2791.
Information can also be provided anonymously via Crimestoppers on 0800 555 111 or by contacting the Police Ten 7 show.