The Brazilian government has written to the Australian Government to express its frustration over the recent acquittal of three police officers charged over the tasering death of student Roberto Laudisio Curti.

The ABC has obtained a copy of the diplomatic note from the Brazilian embassy to the Department of Foreign Affairs and Trade, complaining about a local court decision to clear the policemen charged over his death.

The note, sent in late December, stated: "The Embassy of the Federative Republic of Brazil wishes to convey the frustration of the family of Roberto Laudisio Curti [and] endorsed by the Brazilian government, regarding the results of the judgment concerning police officers involved in the operation which resulted in the death of the Brazilian national."

NSW Greens MLC David Shoebridge said while the note might seem polite in ordinary parlance, in the world of diplomacy it was an extraordinarily strong rebuke.

"It is almost unheard of for another nation to be making this kind of frank and critical assessment of the judicial system and of the police oversight system in Australia," he said.

Curti died in March 2012 after being tasered 14 times, seven times within 51 seconds.

The 21-year-old had taken LSD and stolen some biscuits from a convenience store in Sydney's CBD.

A witness called triple-0 and the operator mistakenly recorded the report as an armed robbery.

Up to a dozen officers chased the bare-chested, unarmed Brazilian student along Pitt Street, before he was eventually pinned down and handcuffed while being repeatedly tasered. He died at the scene.

Four of the policemen involved were charged, two with common assault and two with the more serious offence of assault occasioning actual bodily harm.

Magistrate Clare Farnan found only one of the officers guilty, Senior Constable Damien Ralph. His assault charge related to the use of capsicum spray, not tasers.

She said at the time that "while I accept that in the heat of the moment Mr Ralph may have thought it appropriate to continue to use the third bottle of OC [capsicum] spray ... it is obvious that it was not".

But she accepted Mr Ralph had suffered psychologically and agreed not to record a criminal conviction against him.

The other three officers, all of whom deployed tasers on Mr Curti, were found not guilty.

Police acted as 'legal hooligans'

Brazilian ambassador Rubem Correa Barbosa said because the family had previously requested privacy, it would be improper for him to comment on the case.

But speaking to the ABC from Brazil, Curti's uncle Domingos Laudisio said the family were appalled by the magistrate's decision.

"These officers acted as legal hooligans or reborn convict police of early Australia," Mr Laudisio said.

"You need deep changes within the legal and police constitutional framework."

Mr Laudisio said his nephew's death had had devastating consequences on the family, both psychologically and physically.

"Just to give you an example, Roberto's grandmother was in perfect health back in 2012 when Roberto was alive," he said.

"Today she has nervous problems, she has problems with her bones and she has problems remembering things."

Mr Shoebridge said the incident was one of the notorious and shameful cases of police excess in recent history.

"Mr Curti was crash tackled to the ground, he was repeatedly tasered, he was drive stunned, he was capsicum sprayed, he was partially asphyxiated, and much of that happened while he was lying prone on the ground with his arms handcuffed behind him and he died at the scene," he said.

"Now that's obviously an appalling incident that his family and his country want some justice for."

Case highlights 'inherent conflict' of police investigating police

Mr Shoebridge said if the men involved had not been police officers, police would have laid multiple charges, including murder.

"But it's the police uniform that has meant that justice has been so difficult to obtain in this case," he said.

"When you look at the magistrate's reasoning, it's almost as though the police are being held to a different standard to anybody else in the community.

"What is reasonable force when the police are engaged in violence on the streets [is] judged by a far more generous standard.

"There are reasons to understand why police are applying force, but the force in this case, which ended up with a dead Brazilian citizen on the streets of Sydney ... was extraordinary and surely someone should have been held to account."

Mr Shoebridge said the case highlighted the need to end the system of police investigating police when there was a critical incident.

"Whenever you have police investigating police you have an inherent conflict," he said.

"And that conflict of interest means that when the witness statements are taken, the initial investigation is done, there's almost never enough material to end up with a successful prosecution against the police."

A spokesman for DFAT said: "The Australian Government has regularly engaged with the Brazilian Government, following the tragic death of Roberto Laudisio Curti. These discussions have taken place both in Brazil and Canberra."