Justine Ruszczyk's family is deeply saddened by the death of George Floyd in Minneapolis and "greatly distressed" by the way he died with a police officer's knee at his neck.
The Ruszczyks, from Sydney, said their hearts go out to Mr Floyd's grieving family.
"Justine, my daughter, and Jason's sister should not be dead," John Ruszczyk said in a statement to AAP.
"George Floyd, a good man, should not be dead.
"We are deeply saddened by Mr Floyd's death and greatly distressed by the manner in which he died."
Mr Floyd, 46, died on Monday after an arrest on a Minneapolis street.
Video shot on a mobile phone by a bystander showed a handcuffed Mr Floyd lying on his stomach.
He can be heard telling officers he cannot breathe, but officer Derek Chauvin keeps a knee on his neck for almost nine minutes.
Hennepin County Attorney Mike Freeman, after riots, looting and the torching of a police station, announced on Friday Chauvin, 44, had been charged with third-degree murder and second-degree manslaughter.
The three other officers involved in the arrest are also being investigated.
In 2017 Ms Ruszczyk, a 40-year-old Australian life coach and yoga instructor, called 911 for help but was shot dead by police officer Mohamed Noor in an alley behind her Minneapolis home.
A year ago, the Ruszczyks made the long flight from Australia, sat in the front row of a downtown Minneapolis courtroom, and bravely sat through heart-wrenching testimony and horrific autopsy photos.
They watched as Noor was convicted by a jury of the same charges Chauvin faces: third-degree murder and second-degree manslaughter.
Noor is serving a 12.5 year prison sentence.
The Ruszczyks also won $US20 million ($A30 million) after filing a civil lawsuit against the city of Minneapolis.
The family's hope was Noor's conviction and the hefty payout would end the US city's horrific record of police brutality.
"The fact that another person has died at the hands of the Minneapolis police using excessive force shows that they have not made adequate changes to their practices and training as we had been told they would after Justine's murder," the Ruszczyks wrote.
"There is obviously much work to be done."
Mr Floyd was arrested after a shopkeeper reported to police a man had used a counterfeit $US20 note to buy merchandise.
Mr Floyd was sitting in a vehicle near the shop when police arrived at the scene.
Ms Ruszczyk was in her Minneapolis home on the evening of July 15, 2017 when she heard a woman's screams from an alley behind her house.
Noor and his partner responded to her 911 call and as their squad car idled in the alley Ms Ruszczyk approached in the darkness barefoot and in her pyjamas.
Noor, while sitting in the front passenger seat of his police car, shot across his partner Matthew Harrity, out the driver's open window and fatally struck Ms Ruszczyk in the stomach.
He testified he feared he was being ambushed.