Fiji's Human Rights and Anti-Discrimination Commission is investigating police officers over two separate incidents - one involving a robbery suspect who died during his alleged arrest two weeks ago.
The commission is also investigating allegations about the wrongful detainment of a group of men by police last week.
Human rights chief Ashwin Raj said witnesses claimed excessive force may have been used during Mesake Sinu's arrest.
Police had earlier said Sinu died from injuries sustained after he jumped from a double-storey building during a "robbery gone wrong" on 12 October.
Raj said the commission had also obtained a copy of the Sinu's medical certificate which stated he "suffered extensive intracranial haemorrhage due to (or as a consequence of) a severe traumatic head injury".
He said the certificate also stated that the external cause of injury was "blunt force trauma".
Raj said an official complaint was lodged with his office by a relative of Sinu on 13 October.
He said such "acts of gratuitous violence" must be thoroughly investigated and those responsible must be held accountable through the criminal justice system.
"A life has been lost," Raj said. "This is an egregious violation of the victim's right to life."
Four men detained after seeking police help
Four men claimed they were arrested by police last Friday for an alleged breach of the Covid-19 daily curfew, which is from 11pm-4am local time.
The grouped claim they couldn't locate a taxi to take them home after work and had gone to the police station for help.
Instead the men said they were detained by the officers.
Raj said he was concerned the men were not released for 18 hours.
He said this was a violation of their rights and freedom under the constitution.
"When they were taken in for 18 hours did they have the right to contact their family members, did they have the right to consult a lawyer to say look I am in trouble with the law. I am just wondering if any of these things happened," Raj said.
He said the alleged actions of the officers involved were unacceptable.
Acting Commissioner of Police Rusiate Tudravu has ordered an internal investigation into the incidents.
Tudravu said those found responsible would be charged and produced before a court of law.