Mr Dalton's mother, Christine Bowker Wilson, said she believed the investigation into her son's death needed to include those working at the prison at the time of his death. In Samoa, the police also oversee the prison.
She said she was concerned the man who had been charged - believed to also be a mental health patient - would be kept at the prison while waiting on court hearings.
"We have concerns for his safety. Our biggest priority at the moment is trying to ensure the safety of that young man."
Mr Dalton travelled to Samoa on December 11 with family for the unveiling of a headstone. His mental health was good, he was being treated with clozapine and doctors considered him able to travel.
Two days after their arrival, Cyclone Evan left Samoa in chaos.
Mrs Wilson said her son missed two doses of medication, which led to the gradual slide of his mental health.
On December 23, help was sought from Samoan health authorities and Mr Dalton was taken into care at the converted carport serving as an acute treatment centre.
Mrs Wilson said different medication exacerbated Mr Dalton's psychosis and led the mental health workers to seek police support. He was taken to police cells, when sister Natasha Dalton saw him on Christmas Day, shortly before he was taken to prison.
"Tash, am I going to be okay?" she recalled him asking. "I told him, 'Yes', he would," Ms Dalton said. Within 24 hours, he was dead.
Mrs Wilson said she questioned the suicide finding on Boxing Day after seeing her son's body.
"He had been brutally bashed."
Assistant Police Commissioner Le'aupepe Fatu Pula confirmed the arrest of the 21-year-old, who was being kept at the jail when Mr Dalton died. He did not believe either man's cell had been locked.
