Victoria's hotel quarantine inquiry on Monday heard the fateful decision to use guards was likely made at a meeting at the state control centre on the afternoon March 27.

But the decision wasn't made by one person or government department.

Rather, counsel assisting the inquiry Rachel Ellyard said it was a "creeping assumption that became a reality".

"While no one person made a decision, by the end of that state control centre meeting, it was understood by all present that that was what was going to happen," Ms Ellyard said in her closing submission on Monday.

In that meeting, Victoria Police Assistant Commissioner Mick Grainger said it was the force's "preference" that private security be used.

Emergency Management Commissioner Andrew Crisp stepped out of the meeting to take a call from Victoria Police Chief Commissioner Graham Ashton.

Mr Crisp then texted Mr Grainger: "I stepped out to speak to Graham and I let him know you're in this meeting... He made it clear ... that private security is the first security option at hotels/hotels and not police".

Ms Ellyard said Victoria Police's preference was a "substantial contributing factor to that creeping consensus".

"The expression of a preference can readily be understood to have given the clear impression that police weren't going to do it and there needed to be an alternative," she said.

Ms Ellyard said once the decision had been made, no one in the meeting gave "any specific consideration" to the suitability of private security for the role.

Contracts written up by the Department of Jobs, Precincts and Regions left infection control and training in personal protective equipment use to the security companies.

Hotels, meanwhile, were responsible for cleaning, unless a returned traveller tested positive to COVID-19.

"Responsibility for managing the risk of infection and providing for the safety of those involved in the program should have remained with the state. No contract should have purported to outsource those matters," Ms Ellyard said.

Victoria's second wave of coronavirus can be traced back to outbreaks among security guards and staff at the Rydges on Swanston and Stamford Plaza hotels in mid-May and June.

It led to more than 18,000 new infections and 750 deaths.

Counsel assisting Tony Neal QC said there was no suggestion those who set up the program worked other than with "the best of intentions and to the best of their ability".

"Bad faith or corruption is not what the evidence shows," he said.

"Yet it is true that the hastily assembled program failed at two locations within approximately two and a half months and with disastrous consequences.

"A multitude of decisions, actions and inaction, many of which compounded the effect of the other, ultimately expressed itself in the outbreaks which subverted the very reason for the existence of a hotel quarantine program.

The three lawyers for the inquiry will each make submissions on Monday, before the $3 million investigation hands down its findings on November 6.

Retired judge Jennifer Coate heads the board of inquiry.

Australian Associated Press