Police are searching for a person known as 'Scorpio' or 'Bullit' who has sent more than 100 letters over the past decade to a wide range of high-profile people, including federal and state parliamentarians.
NSW Police say they are working with the Australian Federal Police (AFP) to identify the author of the messages sent between 2015 and 2026, who they believe is Caucasian and in their 60s.
The revelations have prompted Independent Senator Lidia Thorpe to argue authorities "need to be more honest with the public about what they are dealing with".
"When people are targeted because they are Aboriginal, Muslim, migrants or people of colour, police and authorities should not shy away from naming racism, Islamophobia and white supremacy," said Senator Thorpe, who has received letters threatening violence towards her.
"It's notable that today's public statement made no mention of the racist, Islamophobic and white supremacist content contained in these letters. It is hard to trust that police are taking these threats seriously when they are unwilling to accurately describe them."
Strike Force Yewrangara has been set up by NSW Police's Security Investigations to uncover who is behind the letters, alongside the AFP's National Security Investigations team.
"The printed handwriting featured in the correspondence consists of the prominent capitalisation of the letters 'F', 'L', 'T', 'N' and 'H'," a NSW Police statement said.
"The author has also referred to themself as 'Scorpio' or 'Bullit'.
"The author also included newspaper clippings, including snips of headlines and images of prominent people, while much of the writing focuses on matters of national affairs and significant community interest."
Senator Thorpe said the letters sent to her "contained death threats, Nazi symbols and hate against First Peoples, while letters sent to others contained explicit anti-Muslim threats and racist abuse".
"The police had the letters about me on a national threat database for two years before I was even made aware of them. I still have serious questions about why I wasn't notified and what action was taken during that time," she said in a statement.
AFP Superintendent Nathan Robertson said their priority was to prevent any escalation into behaviour that could endanger the broader community.
"We have very real concerns about the content of these letters," Superintendent Robertson said.
"Our investigations are into allegations of criminal behaviour, but we also have concerns about whether the person responsible for them has access to appropriate health and support services."
Senator Thorpe welcomed the announcement on Tuesday, but argued, "there are big questions about why this conduct was allowed to continue for so many years and whether earlier attention could have prevented the ongoing harm or brought this person to justice earlier".
"The public deserves a clear understanding of the level of threat facing First Peoples, Muslim communities, and other racialised communities in this country," she said.
"These threats must be treated with the seriousness they deserve, and governments need to properly resource efforts to combat white supremacist and racially motivated hate before it escalates. That starts with honestly naming the threat."
In May, neo-Nazi Stefan Eracleous, 33, was sentenced to four months' jail in the Melbourne Magistrates' Court after harassing Senator Thorpe, sending messages to her office including references to "White Australia", "white lives matter" and "heil Australia".
During a police interview, Mr Eracleous argued "he wanted to show Senator Thorpe that he was not defeated after having been charged previously" with harassing her, Magistrate James FitzGerald said.
The former Young Liberal — who has links to the National Socialist Network — enacted a "sustained personal attack on Ms Thorpe," Mr FitzGerald said, which "has no place in...a democracy like ours".
