Victoria Police is investigating posters across Melbourne that depict the alleged Bondi terror attack gunman Naveed Akram.
Around 40 of the posters have appeared, featuring an image of the accused shooter and the word "Aussie" written underneath his face.
The posters imitate the style of street artist Peter Drew's popular series, which celebrates multiculturalism.
For more than a decade, Drew's distinctive posters have featured predominantly migrants photographed in the early 1900s with the word Aussie underneath the image.
Melbourne City Council said it has been acting swiftly to remove the posters, with more than 40 taken down in the past week.
Melbourne lord mayor Nicholas Reece said the copycat posters were deeply offensive, saying it was "absolutely abhorrent" that someone had hijacked Drew's art style to create the "terribly distressing images".
The Adelaide artist started the artworks in Australian cities in 2016, using images of people who applied for exemptions to the White Australia policy — a series of laws that restricted non-European immigration to Australia between 1901 and the 1970s.
Speaking to SBS News last year as he prepared to commemorate its 10th anniversary, he said the project's aims were twofold: "I want to reach out to the people who are afraid of people that don't look like them, because that's sort of a part of being human," he said.
He added that he hoped the posters made new arrivals in Australia feel welcome "and that they can belong here as much as I do".
Akram was one of two alleged gunmen who police believe killed 15 people during a Hanukkah celebration at Bondi Beach in December last year.
Police allege Sajid Akram, his father, was the other shooter. Sajid Akram was killed during the incident, while Naveed Akram survived and is now awaiting trial on dozens of charges, including murder and terrorism.
As the councils review CCTV footage, Victoria Police says it's investigating the posters in relation to the offence of billposting. Reece says new state and Commonwealth laws might be applicable.
"We have seen new state and Commonwealth anti-hate, antisemitic laws, those laws are brand new, they're yet to be tested in the courts, so this could be a good test case," he said.
Daniel Aghion, Executive Council of Australian Jewry president, said Australia's Jewish community were "devastated", calling it a "very distressing and very raw image for us right now".
The chairman of Jewish Australian organisation the Anti-Defamation Commission, Dvir Abramovich, hopes those responsible are held accountable.
"If you glorify and celebrate the mass murder in a public space, you should be held accountable. I hope police identify the perpetrators and lay charges, if the law allows, and hopefully they end up behind bars. Anything less invites further escalation," Abramovich said.
The Australian National Imams Council has also condemned the posters.
"It's clear the intention ... [was to] twist it into a message that casts suspicion and hostility over everyday Australian Muslims who want to live in harmony and mutual respect with fellow Australians," it said.
"We reject the intended message behind these posters."
As for Drew, he described those responsible for the copycats as "trolls" seeking to upset people, and that the trick was to "not get upset".
"To get angry in response to their anger ... you fall into a negative cycle."
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