"It comes to the surface, it hurts, it's no fun," he said.
It was heartening to know the case had never died, Mr Percy said.
"The police are putting so many resources into finding who did this, it's great. We will get satisfaction in catching the bastard."
Howard Percy had a successful engineering business in Hastings and when he sold it he bought a farm in Bethlehem, Tauranga. He lived in Tauranga from about 1960 to about 1973. The family lived at Papamoa for a short while before Mr Percy shifted to Rotorua.
Ross Percy said his father was well known in Tauranga and Bethlehem. He was an active sportsman and took the security job in Rotorua because he was "was bored and wanted something to do".
Detective Inspector Tim Anderson said at a press conference in Rotorua yesterday that police had received fresh leads, which led to the decision that a small team of detectives would take a fresh look at the evidence.
He said there had also been advances in science and technology, such as DNA and firearms analysis, which would help the police working on the case.
Ross Percy, and his brother Deryk Percy, from Auckland, were at yesterday's press conference and said they were pleased the case was being investigated again.
They said that, for them, the case had never died. They joined with the police in appealing for information and asked members of the public to come forward if they had any to offer.
The bank Howard Percy guarded was first targeted on July 16, 1976, when a robber tied him up alongside two tellers, before taking about $13,000. The incident was reported in The Daily Post at the time as the city's first bank robbery.
On November 5, the bank was hit again. Mr Percy was again on duty and this time tackled the robber and was shot twice. He died on the way to hospital.
An extensive investigation took place at the time but no one was charged.
A team of officers is now providing what police call "a fresh set of eyes" to the case and is calling for information about the murder.
Mr Anderson said there was no particular suspect but police were interested in a number of people.
"The passage of time doesn't lessen our resolve. In fact, the passage of time can prove very useful as it allows us to make the most of advances in science and technology such as DNA and firearms analysis," he said.
"We are in the process of having all of these items examined using means that weren't available 36 years ago. We are also reviewing all of the original information to identify other possible avenues of inquiry."
Mr Anderson said police had received numerous pieces of information about the case over the years, but a recent piece of new information was what had sparked the fresh appeal for information.
"The time is right ... Not only does science and technology change over time, so do allegiances and relationships. It is possible that someone knew something crucial back in 1976 but their circumstances at that time prevented them from talking to us. Those circumstances may well have changed and we want to make clear it that the door is still open to them."
Rotorua District Councillor Mark Gould worked at the bank at the time and was a key witness to the shooting.
He said he supported Mr Percy's family in urging members of the public to come forward with information.
"It has been a long time and there has been a lot of suffering by all those involved."
Mr Gould said he would expect to do a formal interview with police during their investigation.
"It has been 36 years. I am doing fine, I just hope new information does come forward."
A special phone line and email address have also been set up by police. Anyone with information should ring police on 0800 4 PERCY or they can send an email to operation.percy@police.govt.nz
Alternatively, information can be provided anonymously via Crimestoppers on 0800 555 111.