Casey Dekker, 23, is the fifth person to front court in relation to an alleged drug syndicate that was uncovered while police were investigating the fatal shooting of Nathan Costello on Valentine's Day last year.

Dekker fronted Wollongong Local Court on Thursday charged with commercial drug supply and participating in a criminal group.

In arguing for bail, defence lawyer Matt Russoniello told the court the police case against his client was weak, with the police facts containing "no specifics" about her alleged involvement in the syndicate.

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Police prosecutor Sergeant Tanya Pavlin opposed bail, saying detectives had recorded more than 3000 calls relating to the drug supply allegations and that there was "substantial evidence" of Dekker's involvement.

She said more evidence would be provided in future court proceedings once the phone calls had been transcribed.

Magistrate Michael Stoddart refused Dekker's bail application, finding the police case appeared strong "on face value".

He said he couldn't be satisfied any bail conditions imposed by the court could mitigate the risk Dekker posed to the community if released. He adjourned the case to January 8.

Meanwhile, police made a sixth arrest - a 31-year-old man - on Thursday afternoon and charged him with ongoing drug supply, participating in a criminal group and commercial drug supply. He will appear in court on Friday.

A 33-year-old man has been charged with murder over Mr Costello's death.