The National Party has been accused of being selective of the crimes it cracks down on at the Royal Commission investigating historic abuse in care's public hearing.

Photo: Dr Kim Workman

Twenty-eight witnesses are giving evidence to the Royal Commission into abuse in state and faith-based care at a hearing in Auckland.

Sir Kim Workman joined the police force in 1958 and worked as a youth aid officer in the 1970s. He first visited the Kohitere Boys' Training Centre in Levin in 1971.

"The conditions were so inhumane that they were almost guaranteed to turn vulnerable children and youth into scarred, distrusting and sometimes dangerous adults."

Sir Kim said many of the boys, many of whom were Māori, were taken there for minor crimes - small-time burglary and trespassing.

Police officers at the time believed they were fighting a war on crime, he said.

Visiting the centre made him feel guilty, he told the inquiry.

"I really didn't realise until that time, that what we were doing as individual police officers and social welfare workers was contributing to a situation of institutional racism."

Sir Kim told the inquiry the police culture had improved in recent years - but it was not perfect.

"We've just had examples of that in some of the policies that have emerged in the last week, where the tendency has been to say you've got a problem and we're going to be put more people in and we're going to have more access to firearms and so on."

Sir Kim also criticised the National Party's recently released welfare services discussion document.

The document suggested blocking gang members and their associates from the benefit if they couldn't prove legal income or assets.

Sir Kim said communities were being judged in a way that benefited some and disadvantaged others.

"Requiring them to provide evidence that they're not earning money illegally, rather than having the police prove it, is a significantly retrograde step which is very likely to result in even more crime."

Journalist Aaron Smale, who has investigated the issue of abuse in state care for years, backed Sir Kim's statement.

He accused the National Party of being selective of the crimes it cracked down on.

"I've sat and listened to individuals, including gang members, who have been raped multiple times.

"Simon Bridges was in government for nine years. When did he ever talk about those crimes? When did he ever talk about getting tough on those criminals?"

The hearing will resume for its fourth day in Auckland this morning.