The Murri man died at Logan Hospital on October 2, 2015, after police arrested him at a home in the Logan suburb of Kingston earlier that morning.
Police said Mr Coolwell, who already had injuries, was acting aggressively and was handcuffed for his own safety.
But his family said the 33-year-old had hurt himself and was bleeding so they called an ambulance, and it was paramedics who called police.
Mr Coolwell's family said he was distressed that morning because he was mourning the death of his brother, Bradley Coolwell, who died in similar circumstances in police custody four years earlier.
"This is what’s happening right across the country with the interaction with police and Indigenous people, and we always seem to get the rough end of the stick," Mr Coolwell's uncle, Alfred Coolwell, told NITV News at the time.
"We’ve got to get the messages across to these politicians – it looks like none of them are listening, and it just keeps on happening."
Protestors marched through the Brisbane CBD in the weeks following Mr Coolwell's death, demanding answers from police.