At the Royal Commission police apologised for the second investigation's shortcomings.
The third investigation came after former patient Paul Zentveld, with the assistance of watchdog group the Citizens Commission on Human Rights, successfully took a case to the United Nations Committee Against Torture, which heavily criticised the early-2000s probe.
The committee's decision came out in January 2020 - more than four decades after the ill-treatment allegations first aired.
In late 1976, the Auckland Committee on Racism and Discrimination made public the story of 14-year-old Hake Halo.
Committee founding member Dr Oliver Sutherland said the committee approached National-government Social Welfare Minister Bert Walker.
The minister criticised the committee for making the matter public, saying there was no basis to it.
"He backed down and on December 21 he advised there would be a commission of inquiry led by Auckland magistrate Bill Mitchell."
The committee didn't get the result it wanted.
"The outcome from our point of view was really a whitewash," Sutherland said.
"He exonerated all the authorities that had dealt with Hake Halo. Whether they were Department of Social Welfare, whether they were Department of Health, whether it was Lake Alice, he excused all of the ways in which they handled the boys."
Mitchell did rule, however, that there wasn't express consent for the electric shocks given to Halo.
The boy had said sometimes he was given anaesthetic and sometimes not, and sometimes it was punishment.
"We had always felt that that should never happen to any child and certainly not without parental consent. There was no consent for Hake and Mitchell did admit that," Sutherland said.
More cases came to light; New Zealand Herald journalist Peter Trickett wrote front-page stories exposing what was happening; and chief ombudsman Sir Guy Powles in 1977 published a damning report.
"Sir Guy's report was absolutely uncompromising and said that the boy that he investigated had been served a grave injustice by what had happened to him.
"That really galvanised the politicians, because Sir Guy was Sir Guy. He was the ombudsman, and it was a very powerful statement that Sir Guy made and a very comprehensive report into what was happening at Lake Alice."
Sutherland said after that a police inquiry was inevitable, but no charges were laid when it wrapped up in January 1978.
"[The police report] is interesting for the general feeling of it, which was that children were in the wrong and the staff were largely in the right, and Dr Leeks was in the right."
The children weren't believed.
"Certainly, the bureaucrats and the politicians didn't believe it, or said they didn't believe it.
"It didn't seem to matter what statements the children made and how they all corroborated each other, and they named the same nurses and, of course, they all named Dr Leeks."
Sutherland said Leeks' profession supported him.
Leeks moved to Australia about that time and the unit closed. He continued to work until 2006, when he gave up his medical licence ahead of a hearing into his conduct.
Hawke's Bay man Malcolm Richards was tortured with electric shocks, given drugs and sexually assaulted as a 15-year-old patient in the unit in 1975.
Unaware of the initial police investigation, a few years later he plucked up the courage to visit his local police station to complain.
"I tried to tell the guy on the desk and he just said, 'Look, nothing like that would ever happen in New Zealand.'
"I was shaking because I was extremely frightened of anyone in authority," Richards said
Compounding his worry was the thought he could be sent back to Lake Alice.
"They said, 'Get out of here before we arrest you for wasting police time.'"
His experience wasn't unique.
For 20 years, former patients lived their lives as best they could, until some spoke out.
Former patient Leonie McInroe lodged a claim in 1994. By 1997 RNZ was reporting three former patients taking civil action.
A class action led by Christchurch lawyer Grant Cameron grew and in 2001 the government apologised, paying out just under $13 million to about 200 former patients. Some had legal fees deducted.
As RNZ reported last year, Treasury had earmarked $130m to settle possible claims.
Richards said the settlement lacked rehabilitation for the former patients, something they were still waiting for.
He said Leeks should have been investigated and charged about the time of the 2001 settlement, especially as then-Prime Minister Helen Clark had said, when opposition leader in 1999, that some of what happened to the unit's patients amounted to torture.
Late last year, after their third investigation, police confirmed there was enough evidence to charge Leeks and another staff member who they didn't name, but the pair were ruled medically unfit to stand trial.
A third person, former nurse John Corkran, 89, is charged with ill-treating children. He has pleaded not guilty and faces a trial in the Whanganui District Court.
