Fourth person charged over car park sex attack in Sydney

A fourth person has been charged in relation to the assault of a 16-year-old girl in western Sydney last month.

The girl was allegedly approached by a group of six men in the library on George Street in Liverpool on June 21 and walked with them to a nearby carpark believing she was meeting a mutual friend, police said.

It is alleged the teenager was sexually assaulted in a stairwell and had her mobile phone stolen from her handbag.

A 20-year-old man and two 16-year-old boys were arrested and charged on Tuesday and appeared in court on Wednesday.

Another 20-year-old man was arrested at a Cabramatta home on Thursday night and was charged with aggravated sexual assault and robbery.

He was refused bail to appear at Liverpool Local Court on Friday.