New South Wales police are investigating whether 15-year-old Farhad Khalil Mohammad Jabar acted alone when he shot and killed police employee Curtis Cheng.
Three of the four men arrested in dramatic dawn raids have been released without charge.
An 18-year-old remains in police custody.
They've been questioned following the death of police employee Curtis Cheng, who was shot dead in Parramatta almost a week ago.
The New South Wales Police Commissioner Andrew Scipione told Sydney radio 2GB it's a frustrating process.
"Much happens during the course of arresting them. We search properties, we seize material, we seize equipment. We do a whole range of things that are very useful in the ongoing investigation. But again when we've got sufficient evidence or intelligence to get a warrant we execute the warrant and then we're looking to go to the next stage. If we find evidence at the time we use it. We've taken a lot of material during the course of these searches and that's going to take us a long time to go through."
The effectiveness of the highly publicised raids, which involved over 200 police officers and took several hours, has been questioned by terrorism experts.
Dr Clarke Jones is from the Australian National University.
He says it's important vulnerable young people aren't isolated further from their community.
"As long as we don't further isolate them or marginalise them or label them, that's the worst thing that can happen. It's not all about incarceration, it's not all about charging, it's not all about police. This is a social problem and we need to be dealing with this a bit differently."
Some are looking towards schools and the efforts that can be made by teachers and parents.
Federal Justice Minister Michael Keenan told Channel Nine teachers play an important role.
"Well we're working with New South Wales Education Authorties to make sure teachers who are really on the front line of this actually have the ability to identify if someone under their charge is going through the process of radicalisation and then know what to do with that."
Dr Jones says school programs should start as early as primary school.
"One of the concerns that we all have I think is that the age of the offenders or of people getting involved in violent extremism is starting at around 15. We saw a boy as young as 14 in the UK, through to 24. That's particularly concerning, (for me) as a criminologist: the last thing we want to do is see young kids that age involved in the criminal justice system."
Officials are also making inquiries about the teenage gunman's family.
Immigration Minister Peter Dutton told 2GB it appears Farhan Jabar's family moved to Australia before he did.
"We've had a look at the history and I've asked my department to investigate all of the details all of the applications that have been made."
Mr Dutton says he hasn't seen any information about the shooter's sister, who is believed to have travelled to Turkey in the days before Friday's attack.
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