Australian Institute of Criminology chief executive Michael Phelan said the data would be provided in June because it took one year to compile.

Indigenous Greens senator Lidia Thorpe said the update would not be released until after April, which will mark three decades since the landmark inquiry.

The Gunnai Gunditjmara and Djab Wurrung woman flagged protests coinciding with the anniversary.

"We're looking at major cities being shut down as a result of the increased number of Aboriginal people being killed at the hands of this system," Senator Thorpe told an estimates hearing in Canberra on Monday.

Senator Thorpe clashed with Liberal Jim Molan after he objected to the word "killed" in her question.

"Yeah killed. Did you hear that right? Murdered, genocided, which one do you want?"

Liberal senator and committee chair Sarah Henderson asked Senator Thorpe to ensure she was asking direct questions at the hearing.

"It's relevant as a black woman," Senator Thorpe said.

"This is a reality and nothing's happened in 30 years since the royal commission. People are still being murdered at the hands of the system."

The Greens senator asked how people could be provided with accurate details of Indigenous deaths in custody before the anniversary.

Mr Phelan said he would stick to the statistics rather than the enter into a discussion about the "narrative" she put forward about a racist system.

"Aboriginal deaths in custody are approximately 20 per cent of all deaths in custody, which is reflective unfortunately of the prison population as well," he said.

The institute reports 455 Aboriginal deaths in custody since the 1991 commission up to the end of June last year.

There were 20 deaths in 2018/19, the most recent reporting period.

Australian Associated Press