A man has been charged with the murder of a mentally ill Auckland man who was found dead with his head in a bucket of water in a Samoan prison.

Police intially ruled that Hans Dalton had taken his own life at Tafa'igata Prison on Boxing Day.

Today the Samoa Observer reported that police had arrested a 21-year-old man and charged him over Dalton's death.

Assistant Police Commissioner Le'aupepe Fatu Pula declined to name the man.

"The male is alleged to have assaulted Hans Dalton, causing his death," said Le'aupepe. "The 21-year-old is charged with murder and will appear in the Supreme Court on 28th January."

Dalton, 38, had been visiting Samoa last month when Cyclone Evan struck the country.

His mother, Christine Bowker Wilson, told the Observer her son needed daily medication but when the cyclone hit he was left with no power or water.

He ended up missing two daily doses and was taken to the mental health unit at the National Hospital in Apia.

Bowker Wilson said he was given an injection that made him agitated and very angry.

He punched doors and so the mental health staff sent him to the Apia Police Station.

Yesterday Le'aupepe said when Dalton was referred to the police they held him for a time before he was transferred to the Tafa'igata Prison.

"He became too violent downstairs (at Police Headquarter in Apia) and so he was taken to Tafaigata," said Le'aupepe.

"The thing is the system in place is very poor."

Bowker Wilson saw her son's body in hospital and said he had severe head injuries and bruises all over his body.

Doctors told her his skull had been fractured.

"I know he banged his head on the wall, because people do that when they're in that condition, but if you see someone doing that, you don't just let them - you try and stop them from hurting themselves," she said.

"We were told that the walls at the prison are made of concrete - but even so, we were told by people in New Zealand that Hans could not have been killed that way."

Bowker Wilson said police told her prisoners were calling out, saying they could hear "weird noises" coming from Dalton's cell.

Dalton's funeral was held in Auckland earlier this month.

- © Fairfax NZ News