Corrections officials failed to identify an Adelaide man who died in custody as Aboriginal and a person at risk, an investigation has found.
A report by South Australian Ombudsman Wayne Lines has also criticised officials for failing to provide sufficient information and support to the family of Wayne Fella Morrison and access to him before his death.
Mr Lines has called on the department to apologise to the family and has made a series of recommendations, including the introduction of body-worn cameras in prisons.
"This report includes a number of serious criticisms of the department," the ombudsman said in his findings released on Thursday.
"While I accept that it is easy in hindsight for me to criticise the actions of the department in dealing with an unexpected and high-stress situation, it is essential for the purposes of good administrative practices that I continue to hold the department to a high yet achievable standard."
Mr Lines said it concerned him that senior officials were initially reluctant to acknowledge that the department's dealings with Mr Morrison's family could have been handled better.
"I consider that there were serious shortcomings in the department's dealings with Mr Morrison's family," he said.
Mr Morrison died in 2016 after being restrained and put facedown in a prison van at Yatala Prison in Adelaide's north.
An inquest into the death his death is still in progress and is scheduled to resume next year.
It previously heard he was in custody on assault charges and was being taken for a court appearance by video link when he became involved in a scuffle with officers.
The 29-year-old was lifted into a prison van but was blue and unresponsive when he was pulled out a few minutes later.
Despite resuscitation attempts, he did not regain consciousness and died in hospital several days later.
His mother says after four years she still has no clear answers as to what happened to her son.
"With all the delays in getting to the bottom of my son's death, some changes are required to the law to ensure that parents like me get answers sooner," Caroline Anderson said in a statement.
"An apology is not enough, but it is the right thing to do.
"It is the beginning of acknowledging that they had a duty to care for my son and that they did wrong to him."
National Justice Project director George Newhouse said the corrections department was responsible for Mr Morrison's care while in custody and let him and his family down.
"I appreciate that an apology from the department is a good start, but is not meaningful without accountability and real change," he said.
Australian Associated Press