The family of a 99-year-old man who died after an assault in a Hamilton rest home say they don't want his attacker - who has dementia - to face charges.

Police have finally released the name of the victim of the assault last October. He was Leonard Ralph Hewgill.

Hamilton police - who are still investigating the homicide almost a year after it happened - had refused to release his name but did so after Stuff appealed to the commissioner's office.

Hewgill died on October 6, 2018, a couple of days after he was assaulted in his room at the Hilda Ross Retirement Village by another resident.

Had he lived, he would have received a letter from the Queen marking his 100th birthday last April.

Hewgill's daughter, Leonie Hopkins, said the resident went into her father's room in the special care unit in the evening when everyone was getting ready for bed.

"The staff heard dad call out 'get out, get out, this is my room'."

By the time they arrived, he'd been knocked unconscious. He died in hospital a couple of days later.

Although he'd been diagnosed with dementia, Hopkins said, her father was otherwise in quite good health and was looking forward to his letter from the Queen.

"He asked me once, 'do you think they will give me a party?' "Of course', I said." 

She said her father was a "railway legend", one of the last Taumarunui locomotive drivers.

Stuff has now identified six cases of homicide since 2013 where the alleged offender was a dementia patient, including the first case this year, where Edmund Alan Jenkins, 75, was declared unfit to stand trial for the killing of Edith Roderique, 70, of Ōtaki at a rest home in Raumati Beach.

Experts say more such cases are likely as the population ages and more people are diagnosed with dementia.

Police are refusing to say where they are at with their inquiry into the Hewgill killing, or whether charges are likely.

But Hopkins said they'd indicated to her that charges wouldn't be laid because of the man's mental state, which she was happy with.

"I don't want any charges laid against this man at all.

"It's most unfortunate because these people have no idea what they're doing. The other family are absolutely devastated. I feel so bad for them."

The family of the alleged offender, who is 71, said their aroha went to Hewgill's family.

"It was a horrible incident that we are deeply saddened by, and hope no other family has to go through this ever again while their loved ones are in a rest home."

They said the man, who Stuff has chosen not to name at this time, was once a well-known boxer in his small town and fitness was his passion.

Even as he got older, he was still in "incredible" shape, a granddaughter said, but he was diagnosed with Parkinson's disease in the early 2000s.

The family began noticing he was forgetting things, repeating himself and showing signs of paranoia and aggression.

"He...knew what was happening with his mind and would often get frustrated with himself," the granddaughter said.

He was assessed at Waikato Hospital, diagnosed with early-onset dementia and told he needed to go straight into residential care.

"To us, he was still young, fit and healthy. He still had his witty sense of humour and he still recognised us. But his mind was slowly going."

She said her grandfather spent time at two rest homes before a vacancy came up at Hilda Ross in March, 2016.

"We were told this was the best facility for his needs, a high dependency unit.

"He was a lot younger than a lot of the other patients. He was also a lot more mobile and active - but he simply didn't know where he was or what he was doing there."

His wife would visit him every day, making friends with the other families, residents and staff and acting almost like another carer, sometimes defusing situations between residents. 

"We are a very involved family. We immersed ourselves in the home."

The wife couldn't be there at night, however, and worried that if her husband ever got lost and ended up in someone else's room, he would become disorientated and frustrated.

"I know there were a few incidents where he had an altercation with other patients living there over the three years."

After he attacked Hewgill, the man was taken to Waikato Hospital where he stayed for over a month before being transferred to a specialist high dependency unit.

"As a family we felt great sadness, we felt responsible, embarrassed and guilty," the granddaughter said.

"A lot of us knew Len and often engaged with him when we were at the home. There were a lot of tears for many reasons. And we know that papa had no idea what had happened that night."

She said he was now in a smaller unit where the staff-to-patient ratio was better.