No charges were laid after police investigations in 1977 and 1978, and from 2002 to 2010.
Leeks is now aged in his 90s and the commission was told he is in poor health.
At the commission in June, detective superintendent Tom Fitzgerald apologised for past failings.
"Police accept that in the 2002 to 2010 period police did not accord sufficient priority in resources to the investigation of criminal offending at the child and adolescent unit at the Lake Alice psychiatric hospital," he said.
"This resulted in unacceptable delays in the investigation and meant that not all allegations were thoroughly investigated."
He promised the present investigation would be comprehensive and thorough, saying he expected meetings with Lake Alice survivors would be held in early July, where they would be told of the outcome.
But, four months on, this hasn't happened, and Covid-19 restrictions since August have caused delays.
Hawke's Bay man Malcolm Richards, who spent two months at Lake Alice in 1975, said the delays were frustrating. He has ACC claims and one before the United Nations that could hinge on what police find.
He can't see why police can't hold meetings virtually.
"I suggested that, but they said there's a lot of people who haven't got the technology or haven't got computers and couldn't access it, and I said they could just go into their nearest police station and surely an officer in an interview room can set up a laptop so they can take part. It's not that difficult...
"Zoom is face-to-face in these times. You're looking at the person. You can ask them questions. They can speak to you. It's no real [difference] to me. In fact it's probably less stressful, and by holding back and delaying, everything's held up."
He was 15 when he was sent to the Rangitīkei institution, near Marton, because he had depression.
Richards said he was subjected to electric shocks, including to his genitals, given drugs, and he suspects he was raped.
He told the commission children had died after receiving electric shocks.
He first approached police to complain 41 years ago.
Richards lives with the ongoing effects of his treatment, including experiencing social anxiety and finding it difficult to make friends because he doesn't trust people.
"I have a lot of memory problems from all the ECT. [They've] cost me jobs, and just communicating with people is very difficult because you lose your train of thought all the time, so you just avoid these sort of situations quite a lot."
Wellington man Steve Watt also first complained to police years ago.
He was at Lake Alice when he was 15 and 16 in the mid-1970s.
He said he was given paralysing drugs and forced to watch another boy undergo unmodified ECT, electric shock therapy with no anaesthetic.
Watt isn't confident Leeks or anyone else will face charges from the latest police probe.
"They've set up so many inquiries. If they were going to do anything by now they would have, really.
"I honestly think they're wasting our time."
But he planned to attend if police held meetings with survivors, so he could hear firsthand what was said.
Horowhenua man Rangi Wickliffe was at Lake Alice in his early teens, in 1972 and 1973. He suffered years of abuse in state care.
He said he was subjected to electric shocks, raped, and told his parents didn't love him when at the psychiatric institution.
Wickliffe said the wait for police was stressful.
"We have waited so long for this to proceed forward and now we're at a point where they're not even telling us anything at all actually in regards to the investigation and what's happening.
"It would be a lot more settling for myself if I knew."
Wickliffe would rather see the Crown apologise and pay compensation than have Leeks prosecuted.
Police referred RNZ to an August statement saying the investigation was delayed because of Covid restrictions.
- RNZ
