On this occasion they were called because he was lashing out at staff in the home.

Jack was marched outside by Senior Constable John Whichello.

Only a couple of days earlier, Whichello capsicum sprayed Jack near the same house. There was worse to come.

Whichello slammed Jack into the wall, grabbed him around the back of the neck, and asked him if he remembered what it felt like to be sprayed.

He told Jack that if he got another call to the home he would "empty the whole can into him and shove the can up his arse". Then he punched him in the ribs, and left. Jack started to cry.

When the officers were back in the police van, Whichello asked his partner – who had only been a constable for three months – if they "minded the odd kidney punch?"

It was, according to Assistant Commissioner Brett Guerin, a particularly troubling case. Senior Constable John Whichello was later dismissed.

Mr Guerin is overhauling the police complaints process.

"That's exactly the type of behaviour we don't need: a senior constable, training a constable, punching a kid in handcuffs, at a DHS house, with staff there," he said.

The Victoria Police complaints handling process has been rounded on for more than a decade: first by the Office of Police Integrity; then by Jack Rush, QC, in his inquiry on the ructions between former chief Simon Overland and his deputy Sir Ken Jones; and most recently by the Victorian Equal Opportunity and Human Rights Commission, in a report on predatory sexual behaviour in the force.

Finally, progress is being made, Mr Guerin says.

The process has been simplified and expedited, with complaints triaged into three categories: those which are not criminal and do not warrant dismissal, those which are not criminal but may warrant dismissal, and those which may be criminal.

When Mr Guerin started about two years ago as head of the internal investigations unit, known as professional standards command, one of his first tasks was approving the criminal brief to charge Leading Senior Constable Timothy Baker with murdering a man during a routine traffic stop in 2013. The now former cop was found not guilty on Friday.

But less serious investigations required just as much attention, to ensure they were not taking months or even years to finalise. And the force is starting to respond to the new broom.

"In a sense we're leading and the rest of the organisation is catching up," he said.

"The development of our people is probably lagging on what we're asking of them. We can be a bit like an aircraft carrier."

Mr Guerin said the new complaints process could result in fewer police being formally disciplined.

The vast majority of complaints, he says, relate to what he calls service delivery issues; police didn't show up, an officer was rude, police didn't take a report, police put handcuffs on too tight, police pushed me when they didn't need to.

He is encouraging these complaints to be dealt with in seven days.

"We're moving towards a less punitive discipline system but the intuitive push-back from that is that 'You're going soft on cops'.

"But the sky hasn't fallen, complaints are not going up, in some areas they're going down, and community confidence is still [high]."

While the number of complaints remains static, or have fallen, 32 police were charged with criminal offences last year. Serious internal investigations are ongoing, including into the Inflation nightclub shooting.

Further changes could also be made to how police are investigated, with a parliamentary committee inquiring into the external oversight of police corruption and misconduct.

Forty-three submissions have been made to the joint committee into the Independent Broad-based Anti-corruption Commission, including several that back the establishment of a new body to investigate police complaints.

That suggestion has been dismissed by the Police Association, which also called for IBAC to no longer have powers to publicly interview officers as part of its inquiries.

* Name has been changed

- The Age