Te Aho says Hapuku's sentence was "nowhere near" long enough.
He and has consistently campaigned for harsher sentences for criminals since, including signing a "Justice for Moko" petition to the Parliament in 2016 asking to outlaw plea bargaining practice when it comes to murder charges.
When Hapuku was released on July 29, probation advised Mikara's family about it.
Te Aho expected to be one of them, and says he wasn't aware of the Parole Board's victim notification register.
"To be honest my first reaction was shock and horror then quickly followed by an extreme sense of anxiety, hurt and depression," Te Aho said of seeing it on Facebook.
"I broke down instantly filled with some negative emotions. Not being told of his release by anyone I was extremely shocked, confused and hurt thinking surely this is something someone would warn you about.
"How did they not think 'aw, this violent criminal is being released into society', and not inform the families of the victims.
"My anxiety is through the roof. This puts my job at risk. I do building maintenance all over Manawatū and our work stretches from Wellington all the way up past Hawke's Bay."
Hawke's Bay Today approached the Parole Board and Corrections NZ on Friday and Te Aho, who now lives in Manawatū, then received an apologetic call from probation.
A New Zealand Parole Board spokeswoman said Te Aho had registered on its victim notification register on July 28 which was both after the hearing and after the decision was released to those on the register on July 21.
"A copy of the decision is being sent to Te Aho and now that he is a registered victim he will be kept up to date about the offender."
Victims of certain serious crimes can apply to the police for inclusion on the victim notification register, the spokeswoman said.
Trent Owen Ngaruhe Hapuku, 21, pictured at his trial on August 8, 2011 held at the Napier Courthouse. Photo / File
Te Aho said the justice system was "broken" and Hapuku should not have been released at all.
"It pretty much tells everyone our children don't matter, these crimes don't matter," he said.
"Nine years for my son's life is nowhere near enough for brutally killing my 5-month-old son. It should have been life.
"How are we supposed to change our shocking statistics if the sentences don't reflect the severity of the crimes?"
Te Aho said Mikara was "the most happy child ever".
"He never cried, was always smiling and happy and loving. For Trent [Hapuku] to get upset with him at all even these many years later still just confuses me extremely," he said.
"And I think this really showcases the extremely disturbing person he is.
"He should not be free, he should not have a chance to hurt another child, he should not have another chance at life when my son's life was ended pretty much without remorse."
SIDEBAR:
WHY HAPUKU WAS RELEASED
The Parole Board's decision, made on July 13, noted Hapuku had completed a dependency treatment programme and 22 sessions one-to-one with a psychologist.
The board noted that Hapuku spoke well and said that over his time in prison he had grown up.
They were satisfied that he could be released for a short period of time on parole without posing an undue risk.
It was acknowledged that his offending was "very serious".
However, the board noted that Hapuku had completed treatment in prison to reduce his risk of reoffending and he had informed support in the community.
