Police are continuing investigations into the death of two-year-old Bea Daleon in April 2012.
The toddler was rushed to hospital after suffering a seizure and it's understood she also had a fractured skull.
Police told the girl's parents the circumstances surrounding the death were suspicious.
Inspector Mike Bowman said a large team worked on the case initially and staff are still working on it now, years later.
"Cases such as this are however typically complex and take time to investigate," Insp Bowman said.
"In this case, it has involved inquiries both in New Zealand and overseas, including seeking relevant medical expertise. We are also continuing to liaise through Interpol with the relevant international authorities as part of our inquiries.
"In the meantime, we remain committed to progressing the investigation and building evidence that will support the case."
Police say they are not going to comment on individuals they are considering as suspects at this time.