The Tongan police commissioner says two police officers charged with assaulting a New Zealand police officer who later died may have charges against them upgraded.
Constable Kali Fungavaka, 38, was arrested for drunkenness in Tonga on August 17 and allegedly assaulted by two local police officers before being taken to a police cell.
He was then allegedly assaulted by another man being held in the same cell and died six days later in hospital.
Commissioner Grant O'Fee told Fairfax charges against the police officers could be upgraded.
"There will be an absolutely thorough and robust investigation and there is a whole lot of work still to be done," he said.
"Don't assume these are the final charges."
He also told local newspaper Matangi Tonga that it was distressing to think police may have failed in their duty of care and said Australian police were overseeing the investigation to ensure transparency.
"If they think and say this stinks and we have not done a proper job it will be shown in their report, which will be made public," he said.
Cellmate Semisi Kalisitiane Manu appeared in Nuku'alofa Magistrate's Court on Monday charged with murdering Const Fungavaka.
The two police officers have been charged with common assault.
All three men were remanded in custody to reappear on September 24.
Earlier Magistrate Pita Soakimi asked why only Manu had been charged with murder while the two policemen - named as Salesi Maile and Fatai Faletau - had not been similarly charged.
Const Fungavaka was awarded a New Zealand Bravery Medal in 2006 for saving a burning woman at an Auckland petrol station, an incident which prompted him to join the police.
Const Fungavaka, of south Auckland, was in Tonga attending his grandfather's funeral.