The man, known only as Noomba for cultural reasons, died in custody in Townsville on February 10 after what police described as "an altercation" with officers.
Lawyer Stewart Levitt says Noomba's partner of 19 years, Regina Matheson, called the police and an ambulance when her husband began talking about suicide, possibly fuelled by a substance addiction.
Mr Levitt claims police officers "spear-tackled" the 39-year-old as he left the house to buy cigarettes, pushing his face into the dirt, straddling his back and bending his wrists backwards. He died soon after, while his young children were watching.
In a written statement, Mr Levitt alleges that Ms Matheson told police of Noomba's had a pre-existing heart condition.
Townsville shaken by second death in custody in six months
"Subjected to the very rough treatment which has been described and the shock of it all, it is quite foreseeable that a man with a pre-existing heart condition would succumb," he said.
"What training have Police received in dealing with severely depressed and mentally impaired members of the public, let alone such people who also happen to be Indigenous?"
Footage captured by police on body-worn cameras is likely to be critical when the death is examined by a coronial inquest.
According to Mr Levitt, the man's family claim they were verbally abused by police, who later "ordered" the family out of their home, declaring it a crime scene, despite the arrest taking place on the street.
Townsville Police Chief Superintendent Kev Guteridge said the death occurred during a "reasonably routine" callout.
"Sadly during the taking of that man into custody, he lost consciousness," he said on Saturday.
"An ambulance was present at that time. Despite extensive attempts by police and paramedics to revive the man prior to his transport to Townsville Hospital, those attempts were unsuccessful and unfortunately, the man was unable to be revived and tragically lost his life."
A Queensland police spokesperson declined to comment further, as the matter is currently being investigated by the coroner.
