Nathan Reynolds was "begging for help with his eyes" before he died from an asthma attack in a Sydney jail, an inquest has heard.
Fellow inmate Aaron Robinson fought back tears as he recalled desperately trying to assist the 36-year-old Indigenous man, who went stiff while struggling to breathe in the prison's minimum-security wing on the night of August 31, 2018.
"I needed to keep him calm. He was in a panic, couldn't exhale - he was a man begging for help with his eyes and he couldn't say a word," Mr Robinson told the NSW Coroners Court on Tuesday.
"What little breath he had was just gasping for help.
"He was hunched over with his elbows on his knees leaning forward. I just asked him to look at me and concentrate on me ... to try and relax so he could breathe."
Mr Robinson, trained in first-aid, said another inmate tried to place Mr Reynolds into a wheelchair so the father-of-one could be moved to the jail's clinic, about 40 to 50 metres away, following instructions from a corrective services officer.
But Mr Reynolds' body stiffened up and eyes went "vague" before he broke into a "violent but short fit," Mr Robinson told the court.
Mr Robinson, then 44, was told to roll Mr Reynolds on his back before moving away to allow the prison nurse to treat him.
"I didn't want to let (Mr Reynolds) go ... when they asked me to leave Nathan I knew he was already gone," Mr Robinson said.
The inquest on Monday was told by another inmate, Jeremy Preo, that the Indigenous man was slapped in the face by the only registered nurse at the South Windsor prison that night, Kasey Wright.
Mr Preo also recalled Ms Wright telling a prison officer the dying man was having a drug overdose.
Ms Wright is due to testify later in the inquest.
CPR began shortly after Ms Wright's arrival, continuing when paramedics showed up about 12.14am.
Thirty minutes later, and 77 minutes after he first radioed prison guards about his breathing difficulties, Mr Reynolds was declared dead.
The inquest is expected to hear from respiratory specialist Greg King that when Mr Reynolds radioed for help at 11.27pm, his condition was already severe and life-threatening and the window to prevent his death was very narrow.
Ms Wright wasn't called until after 11.40pm, when the prison officers arrived.
Mr Reynolds' sisters, who attended Monday's hearing alongside her brother's partner and mother, said they want truth and justice.
"Nathan died on the cold floor of a prison, with no loved ones around him. He was just 36 years old - he died far too young," Taleah and Makayla Reynolds said in a statement.