Victoria Police confirmed that it would not proceed with charges against the police officers involved, on advice from the Office of Public Prosecutions.

South-west Indigenous leader Uncle Lenny Clarke said the decision was devastating.

"This goes against the court, the people, social justice and what normally is a societal expectation," he said.

"It send the wrong message to the public and downgrades efforts to seek better relationships between Aboriginal and policing communities.

"The Aboriginal people wanted to see justice for dear Ms Day."

In a statement Ms Day's family said it was "devastated" and "angry". The family called for an independent investigation into Aboriginal deaths in custody.

Ms Day, a Yorta Yorta grandmother, died after sustaining head injuries when she fell in a cell at Castlemaine police station on December 5, 2017.

A coroner found in April that an indictable offence might have been connected with Ms Day's death.

Coroner Caitlin English found police officers in charge of custody that day, Sergeant Edwina Neale and Leading Senior Constable Danny Wolters, performed inadequate checks on Ms Day while she was in custody.

Ms English ordered the matter be referred to the Director of Public Prosecutions.

Victoria Police confirmed on Thursday it would not be laying charges.

Ms Day's family called for the state government to commit to an independent investigation of deaths in custody, in response to the decision.

In a statement, the family criticised the Office of Public Prosecutions, saying it seemed to have based its conclusions on a police investigation that was flawed and lacked independence.

"It is not good enough that such an important decision was made behind closed doors without any input from our family or the broader Aboriginal community," the family said.

"It is in the public interest - and the interests of Aboriginal people across Australia - that the police be held accountable for their actions."

"In the last 30 years, hundreds of Aboriginal people like our mum have died at the hands of the police, yet no police officer has ever been held criminally responsible."

The family said it hoped the worldwide Black Lives Matter movement might have led to care and accountability for their mother's death.

It said the Director of Public Prosecution's decision not to prosecute was wrong and spoke volumes about systemic racism and police impunity in Australia.

"Aboriginal people will keep dying in custody until the legal system changes and police are held accountable," they said.

In a statement Victoria Police said it acknowledged the loss and suffering experienced by Ms Day's family.

"Victoria Police takes any death in police care or custody very seriously and will continue reviewing the coroner's findings and recommendations," it said.

"All coronial findings provide an opportunity for Victoria Police to review its policies and practices to ensure the safe management of people in police care or custody."

Ms Day was travelling from her home in Echuca to Melbourne, first by coach to Bendigo, then by train.

Shortly after leaving Bendigo, the conductor began checking tickets and came across Ms Day lying on the seat, with her feet across the aisle.

He asked for her ticket and destination, to which she gave unrelated answers, and he determined she was an "unruly" passenger under V/Line guidelines.

The conductor contacted the driver to call police, which necessitated the train making an unscheduled stop at Castlemaine.

At Castlemaine railway station, two officers boarded the train and found Ms Day asleep.

When roused, her replies did not make sense and she smelled of alcohol, so they arrested her and removed her from the train.

Ms Day was taken to a cell at the police station at 3.56pm.

The sergeant on duty requested Ms Day be checked every 20 minutes, but at some point the sergeant and the watch house keeper agreed to change this to every 40 minutes, requiring a verbal response from her every second check.

At 4.49pm the watch house keeper checked on Ms Day through the window.

One minute later, she got up, stumbled and hit her forehead hard against the wall - this was not seen by police at the time, but later observed on CCTV.

She tried to sit up, but her right arm seemed unable to support her and she appeared to again hit her head.

These were among a number of falls that day.

Between then and 8.03pm, Ms Day was observed four times on the monitor and twice through the cell window - both times, the watch house keeper recorded that he had received a verbal response from her.

It was at 8.03pm that the watch house keeper and sergeant went to see Ms Day with the intention of releasing her.

They noticed a bruise on her forehead, and to some questions Ms Day only groaned.

Paramedics were called and Ms Day was taken to Bendigo Health, where it was discovered she had a bleed on the brain.

That night she was airlifted to St Vincent's Hospital and underwent surgery, but died on December 22.

Ms Day was the second person in her family to die in custody - the 1982 death of her uncle, Harrison Day, was examined in the Royal Commission into Aboriginal Deaths in Custody.

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