The murky past of the 20-year-old business student can be revealed as disgraced former detectives Roger Rogerson and Glen McNamara are behind bars charged with his murder.

Two days after his body was found wrapped in a blue tarpaulin off the coast at Cronulla, his girlfriend visited the site on Wednesday and threw flowers into the ocean near where her ''babe'' was discovered.

Friends said they were in ''absolute shock'' that the credit-average student, who came from a good family, had been murdered.

''A lot of his friends didn't know that he did drugs, we were really shocked about it,'' a close friend told the Herald.

But Fairfax Media can reveal a week before he disappeared, Mr Gao was in the Downing Centre Local Court accused of kidnapping a young man with two others at Carlton in Sydney's south.

The University of Technology student allegedly forced the victim into a car and detained him in a bid to get information about a relationship breakdown in January.

Mr Gao originally faced Kogarah court, the same courtroom where one of his alleged killers, Mr McNamara, appeared on Monday charged with murder and large-scale drug supply.

Police will allege Mr Gao took three kilograms of the drug ice to the pre-arranged meeting with Mr McNamara and Mr Rogerson at Arab Road, Padstow, on May 20.

The trio then allegedly drove a short distance to a storage unit where Mr Gao was allegedly shot twice in the chest before his body was stuffed into a silver-coloured surfboard bag and later dumped into the ocean.

Senior police sources say the investigation into the botched drug deal continues. They say detectives are yet to speak to two men of Asian appearance who escorted Mr Gao to the fateful meeting in Padstow.

Police have also not yet recovered the gun used to shoot Mr Gao but say they are not seeking anyone else in relation to his death. Detectives are investigating Mr Gao's background and connections and have denied reports he had been working as a police informant at the time he killed.

Several friends of the former Caringbah student said they had no idea how he became involved in the criminal underworld.

An only child, Mr Gao lived in a million-dollar house in Hurstville with his mother, Katherine Gao, who runs a small business in nearby Rockdale.

''He had a lot of friends because he is really friendly, always had a big smile on his face,'' one friend said. ''Everyone knew him and he has always been a good boy at home.''

Another described Mr Gao as a brother, neighbour and friend.

"This person was someone who was great in a lot of ways, but above all, he was always loyal to his friends and family - that's something he taught me over the years," he posted on Facebook. "So no matter how many more years pass, I'll always remember the great times that we had being neighbours, friends and brothers. Jamie Gao, from the bottom of my heart, thank you for growing up with me."

Mr Rogerson was reportedly being held in Silverwater jail on Wednesday but had been denied protective custody due to this area being over populated.

Angered at how the 73-year-old disgraced former cop was arrested at his Padstow home on Tuesday, his solicitor, Paul Kenny, had threatened to complain to Police Commissioner Andrew Scipione and Premier Mike Baird. However, no formal complaint had been lodged by Wednesday night.