Her mother Lisa Kuka was jailed for nine years after being convicted on two manslaughter charges because she failed to protect the toddler from abuse or get medical help when she was injured.
Kuka's partner Wiremu Curtis and his brother Michael Curtis received life sentences with a minimum non-parole period of 17 years for Nia's murder. Oriwa Kemp was paroled last year for her role in the abuse.
Rotorua Mayor Kevin Winters said he was "stunned" to hear Pearson had been released: "People have a fundamental right to know. It was such a high profile case. It was a complex case, it consumed people."
Pearson, whose mother took Nia to hospital after she had been in a coma for 36 hours, was denied parole in November. At his sentencing he was assessed as being at high risk of reoffending.
Pearson was released in June having served his full three year sentence.
Rotorua National MP Todd McClay wanted to meet with Winters to discuss Pearson's release.
"I was extremely concerned to hear of the release of this person without the public being informed. The community of Rotorua continues to feel for the tragic death of young Nia Glassie and many people will be distressed to hear that this person is now out in public," he said.
"He was found guilty of horrific ill-treatment of a child and it was reported at the time of his sentencing that he was a high risk.
"I think it is extremely important our services and other agencies follow up to make sure that the community can be assured that any risk of reoffending has been adequately dealt with."
McClay said Nia's death was "traumatic" for Rotorua but urged people to be fair with Pearson.
"He's done his time ... but he'll have a lot to prove to the community."
Sensible Sentencing Trust Rotorua spokesman Peter Bentley thought the public should be told of any releases in high-profile cases.
Pearson's lawyer Harry Edward said his client was living in Rotorua and working closely with family members on a reintegration programme.
- ADDITIONAL REPORTING: ROTORUA DAILY POST
