Brazilian student Roberto Curti had been calling out for police help just an hour before his fatal arrest, a court has heard.
Mr Curti, 21, died in the early hours of March 18, 2012, after a chase and violent struggle with police in which he was tasered, handcuffed, hit with capsicum spray and knelt on.
Policemen Scott James Edmondson, Daniel David Barling, Chin Aun Lim are accused of using excessive and unlawful force against the student by repeatedly tasering him while he was lying on the ground, surrounded by police.
Prosecutors say their colleague Damian John Ralph unnecessarily used his capsicum spray on Mr Curti.
All four have pleaded not guilty to assault charges.
Security guard Murat Metin, who was working on George Street that night, told the court hearing on Tuesday that he had seen Mr Curti being attacked by three teenagers about 5am.
“They were about 16 to 19 years old … two of them were kicking and another person was hitting (Mr Curti) with his fists when he was on the ground.”
Mr Metin said Mr Curti had called out for help.
“He said ‘polici’ … He was continually asking for help, asking for police … but no one was helping him.”
After the three teenagers left, Mr Metin said he asked Mr Curti – who was still lying on the ground – if he wanted an ambulance or police.
“He quickly stood up and ran away.”
The court has previously heard Mr Curti had become increasingly afraid and erratic after taking the drug LSD with two friends.
By the early hours of the morning, he was seen running around the city before going to a convenience store and stealing two packets of biscuits.
The hearing continues.