Police handling of two incidents is under the microscope.
IPCA refers complaints back to police.
Watchdog will have oversight of investigations.
Complaints made to the Independent Police Conduct Authority over police handling of two unrelated deaths in Waikato have been referred to the police for investigation.
Police laid a murder charge against a 37-year-old man who it was later revealed had been returned to the address by police shortly before the incident.
Emergency services were called to the house at 5.20pm that Sunday and Zahquiel was rushed to hospital.
It is understood his father and another man at the house were also injured.
Police said they verified the accused man - who has name suppression - as having his address being at the Anthony Crescent home in Bader and dropped him off there.
They previously refused to say whether they went inside the house that day or if they were aware a child lived in the house.
Police notified the IPCA of the situation and two other complaints were lodged after Zahquiel died.
On Wednesday, IPCA investigations manager Stuart Graham said the police watchdog was referring the case back to police for investigation with IPCA oversight.
A police spokesperson confirmed it was investigating the matter as a “category B - a police investigation with IPCA oversight”.
“The information obtained from the homicide investigation will be used to assess if there are any learnings or matters that require follow-up.
“There is no timeframe at this stage for when this work might be completed.”
In the second incident, pedestrian Steven Cranston, 43, was fatally struck by a car near Raglan on September 4.
Cranston, who lived near Hamilton, had been seen walking his dog in the middle of the road in and around Raglan early that evening and multiple calls were made to 111 over a 90-minute period.
A woman who made several calls to 111 that night, who asked not to be named, told RNZ she complained to the IPCA because she believed an earlier response from police may have saved Cranston’s life.
The IPCA said it has also referred the matter back to police for investigation with IPCA oversight.
A police spokesperson said police were in contact with the IPCA in relation to the questions they had regarding the incident.