Police will allege Mr Gao was shot dead by former detectives Roger Rogerson and Glen McNamara during a bungled multimillion-dollar drug deal last week.

The University of Technology student's body was found floating off the coast of Cronulla six days later.

But one week before the 20-year-old was killed inside a Sydney storage unit, he faced court charged with abducting a man in Sydney's south "over a girl".

Victim Jaiwei Yu, 19, told the Daily Mail online that Mr Gao and two other men had abducted him from a unit at Carlton in Sydney's south in January this year.

Mr Gao and two friends had reportedly gone to the unit to exact revenge on a man named Alex Li, after he had dumped a girl.

But he was not home so the trio allegedly kidnapped Mr Yu, took him to a park and punched him in the mouth, police said.

"It was because Alex and [his girlfriend] broke up," Mr Yu told MailOnline.

"[She] wanted revenge on Alex. She used Jamie to do it ... to come around and kidnap me."

The intended target told the Daily Mail that Mr Yu had been held captive for 90 minutes, driven around in a car and bashed in Tindale Reserve.

"They drove around, through the park and they beat him up with fists in the head," Mr Li told MailOnline.

Police charged Mr Gao with taking and detaining Mr Yu in company with intent to get advantage and occasioning actual bodily harm.

He was also charged with conspiring with two others to assault Alex Li and to cause him actual bodily harm.

A girl and another minor will face Sutherland Children's Court in July charged in relation to the kidnapping.

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.