Immigration officials are investigating the circumstances in which the family of a 15-year-old who shot dead a NSW Police employee came to Australia.
It appears Farhad Khalil Mohammad Jabar's family moved to Australia ahead of him, Immigration Minister Peter Dutton has told 2GB radio.
But Mr Dutton says he's not seen any information about Jabar's sister travelling to Turkey a day before last Friday's attack.
Three of four arrested in raids released
Three of the four people arrested in pre-dawn raids in Sydney's west have been released from custody as investigations into the killing of NSW police employee Curtis Cheng continue.
An 18-year-old man who was arrested at a home in Wentworthville remains in custody.
It comes after more than 200 armed officers raided homes in Guildford, Wentworthville, Merrylands and Marsfield at 6am on Wednesday, arresting four males aged between 16 and 22.
The 16-year-old and two 22-year-old men have been released from custody, a police spokeswoman said on Thursday.
The 16-year-old and 18-year-old were from Wentworthville; one 22-year-old was from Merrylands and the other was from Marsfield, police said.
They included past and present students of Arthur Phillip High School, the school attended by 15-year-old Farhad Khalil Mohammad Jabar, who gunned down Sydney police accountant Curtis Cheng in a Parramatta street on Friday.
A 17-year-old boy arrested and charged on Tuesday is also a student at the school.
Authorities are almost certain Jabar did not act alone.
At least three of the four who were arrested on Wednesday were also targeted in the sweeping September 2014 terror raids across western Sydney.
NSW Police Deputy Commissioner Catherine Burn said authorities suspect those arrested have some knowledge of Friday's shooting and could have influenced Jabar.
Investigations into Jabar's motivation continue, but Ms Burn told reporters on Wednesday it's suspected "there was some influence" that was of an ideological, religious or political nature.
