Opposing the 20-year-old's application, police claimed two of the man's teenage siblings - who are due to give evidence at his trial - were fearful he would try to contact them if he was released, Wollongong District Court was told.

Senior Constable Stuart Boyle said the pair alleged the man was at the house when the teen died on October 12, 2008 and there were genuine concerns he would try to "interfere" with them.

The man and his 46-year-old female co-accused, who was also charged with being an accessory, formally pleaded not guilty to the allegations last year and are set to stand trial on May 27.

The victim's badly decomposing remains were discovered inside a wheelie bin buried in an elderly woman's northern suburbs backyard on February 28, 2011.

The 73-year-old woman pleaded guilty to the teen's manslaughter last year, admitting to failing to care for the sick girl after she suffered injuries at the hands of an "unknown assailant".

The man, who was 15 at the time of the incident, is accused of helping to dispose of the teen's body.

It is alleged he helped another teen dig a hole in the elderly woman's backyard to bury a "dead dog".

Senior Constable Boyle told the court he was unsure if the man knew where his siblings were living but noted they had seen him as a "father figure" and they were scared he would try to contact them.

He said he could direct the teens to notify police if the man did try to see them but it was "up to them" to report it.

Judge Paul Conlon said he was satisfied the witnesses' fears were real and refused the man bail.

He is set to reappear in court on March 12.