A postmortem report circulating in the courtroom on Friday in Benoni, east of Johannesburg, said 27-year-old Macia died of oxygen starvation.
He also suffered a range of injuries including "extensive abrasions on the face, limbs and body" and bruises to his back, torso and testicles.
Cellphone footage of the incident taken by a bystander showed Macia scuffling with police after parking his vehicle illegally. He is then subdued and handcuffed to the back of a police truck before the vehicle drives off in front of scores of witnesses. He died later in a police cell.
A Reuters reporter in the court heard the driver of the truck, Lungisa Edwaba, tell the court he had not known Macia was cuffed to the back of the vehicle and had only driven off because someone in the crowd had thrown something at him.
The images, which were broadcast around the world, rekindled memories of apartheid-era police abuses and highlighted the alarmingly high number of people who die in police custody in Africa's largest economy.
According to the Independent Police Investigative Directorate, the police's main watchdog, nearly 1 000 people died last year in police custody or as a result of police action.
A few bad apples
Police Commissioner Riah Phiyega blamed Macia's killing on a few bad apples in a massive force.
However, the incident is just the latest in a series of scandals to hit a force already dogged by accusations of brutality, corruption and incompetence.
The lead detective in the murder case against track athlete Oscar Pistorius, Hilton Botha, was removed from the investigation when it emerged he had been charged with seven counts of attempted murder for opening fire on a taxi full of passengers.
Last August, 34 striking mineworkers were shot dead and 78 were injured when the police opened fire while trying to disperse a group which had gathered on a hill near the Lonmin platinum mine. – Reuters