By Wendy Carlisle for Background Briefing, ABC Updated November 3, 2012,
Tommy Wang heard shouting and "zapping" sounds and saw "six to seven police chasing a topless man with his jeans falling down" and then setting upon him in a "brutal" way.
Mr Curti, 21, was tasered 14 times by police and died on the pavement outside a coffee shop in downtown Sydney just after 6.00am on March 18.
He had been wanted by police in connection with the theft of two packets of biscuits from a city convenience store earlier in the morning.
Mr Wang has told ABC Radio National's it was clear Mr Curti was "on the ground already and surrounded by six of the police at least" and that he thought the police "didn't look like police".
"[It's] just my opinion but I think they looked like a gangster mob trying to take down a young guy," Mr Wang said.
He says he was too "scared" to intervene in the arrest.
Mr Wang says police only followed up his first witness statement to police after he gave an interview to the Sydney Morning Herald the following day about what he saw.
Detectives contacted the Herald and obtained Mr Wang's mobile number, and when he told them he had already given his contact details to police they were "surprised", he said.
"I mean they had my contacts and everything and it wasn't until the media got onto it that a whole bunch of different detectives contacted me," Mr Wang said.
New South Wales police have declined to comment.
Mr Curti's death was the subject of a coronial inquest in Sydney last month.
Thirty witnesses, including police, medical experts and Mr Wang, were called to give evidence.
Senior Sergeant Peter Davis, a police tactical training expert who was not involved in the incident, told the inquest the use of tasers by the police was justified and within police operational guidelines
Counsel assisting the coroner Jeremy Gormly SC disagreed, and said the police action was an "act of thuggery" and their use of taser "excessive" and "unreasonable".
The four officers who tasered Mr Curti have not been formally reviewed by the Police Taser Review panel and are still authorised to carry tasers.
State Coroner Mary Jerram will hand down her findings into the manner and cause of Mr Curtiss death on November 14.
Listen to Wendy Carlisle's full report on Radio National's at 8am AEDT Sunday, November 4.