More charges expected over Cheng murder

NSW Police expect to lay more charges after a third man was arrested over the murder of police accountant Curtis Cheng.

Mustafa Dirani, 22, is accused of joining with others to commit a serious violent act leading up to the fatal shooting of Mr Cheng by 15-year-old schoolboy Farhad Jabar outside Parramatta police headquarters in October.

Dirani was arrested in Sydney's northwest on Friday and charged with participating in a criminal group and assisting in committing a terrorist act.

He did not apply for bail and it was formally refused on Saturday at Parramatta Bail Court.

Deputy NSW Police Commissioner Catherine Burn said more evidence surrounding the shooting is coming in and police expect to lay more charges.

Dirani is due to face court again on November 26.