"Energetic fraudster" Rosa Rossi changed locks on six vacant properties without the owners' knowledge.

Three were in the Willaura (about 100km west of Ballarat) and the rest in the Melbourne suburbs of Malvern, Chadstone and Brooklyn.

The 57-year-old took over the houses between April 2016 and June 2017, renting some out and using false documents as well as her job as a police officer to cover her tracks.

She misused the force's database to get information about vacant properties and at one point went to a suburban Melbourne council office in uniform to demand an owner's number.

When a concerned neighbour called police after spotting Rossi at one Willaura home, she said she was an officer, had keys and was buying the property.

Rossi eventually resigned from Victoria Police and pleaded guilty to nine charges including of obtaining property by deception, perjury, and unauthorised access to police information following an anti-corruption investigation.

She was depressed at the time and embarked on the fraud in a misguided attempt to build a property investment portfolio, the County Court of Victoria was on Friday told.

Judge Martine Marich described Rossi was an "energetic fraudster".

"It feels somewhat delusional," the judge also said of the attempt to acquire the properties under a legal process known as adverse possession.

This allows someone to obtain ownership of a property if they can prove they've possessed it exclusively for at least 15 years.

One of Rossi's victims, a disability pensioner, described feeling angry, stupid and used.

After being sprung at the man's Willaura home, Rossi reassured the owner she was a police officer and convinced him to sell her the property.

The sale fell through when Rossi couldn't get a loan and her lies unravelled.

"It didn't seem right to me that a police officer would be up to anything fraudulent," he said.

"I was gutted. I felt like a fool.

"I still don't know why she did this."

Prosecutor Peter Pickering said Rossi acted ruthlessly, misused her position of authority and deserved to be jailed.

She remains on bail working on a farm and as a hairdresser, hoping to line up a job with Coles, the court was told.

She's due back in court on June 12.

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