A former immigration insider says the Christmas Island riot was inevitable given the influx of criminals joining the general asylum seeker population at the detention centre.

Steve Brooker was the national mental health manager for the Immigration Department's medical contractor International Health and Medical Services (IMHS), with responsibility for services on Christmas Island, Nauru and Manus Island.

But he resigned in May to protest cutbacks to staffing levels across the offshore network.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 5 minutes 40 seconds 5 m A former Immigration Department health worker says mixing criminals with asylum seekers is problematic.

"A lot of the tensions and a lot of the issues that we would have been able to hopefully prevent, we lost the ability to do so," Mr Brooker told Lateline.

"Sometimes there's just a match that's thrown onto a tinderbox as has happened this week and things just flare up unexpectedly but also expectedly, because you can generally see that some of these things could have been predicted," he said.

Order has been restored to the remote facility after two days of confrontation between authorities and detainees, who had built barricades, set fires and armed themselves with weapons including a chainsaw.

Reinforcements of Australian Federal Police and Border Force officers helped contain the unrest by using teargas.

The make-up of the population at the detention centre has changed dramatically over the past 12 months.

The Immigration Minister Peter Dutton said there are 199 detainees at the centre currently and that the majority were hardened criminals.

He said many had been convicted of assault, child sex offences, rape and robbery.

The detainees on Christmas Island include New Zealanders who have failed the immigration system's tough character tests.

Criminals 'harder to engage' than asylum seekers: Brooker

Mr Brooker said the combination of criminals and asylum seekers had created new problems for health staff.

He said people who had been through the prison system had different needs to asylum seekers who had come to Australia by boat.

"At the time I left, my concerns were really that we were facing a harder group to engage," he said.

"[They] were going to be more acute because of risk of harm to others or to self, more forensic histories, more drug and alcohol problems, people with security risk, which means they've been in detention for a good few years with a lack of hope."

The riot is said to have been started by the death of Iranian refugee Fazel Chegeni, whose body was discovered after he escaped the facility.

Mr Chegeni was found to be a refugee but was convicted of assaulting another detainee at the Curtin detention centre.

His supporters said he lived in the community in Melbourne for a time before ending up on Christmas Island.

Mr Brooker said the Immigration Department needed to thoroughly investigate Mr Chegeni's death and bolster mental health staff at the centre.

"It will happen again in the future if we don't deal with this in a proper way," he said.

Former Christmas Island administrator Jon Stanhope criticised the Government for not providing more detail about how Mr Chegeni died.

"It's blatant nonsense to suggest that a politician can't speak about the death of somebody within your care and control and custody as a result of the need for the matter to be referred to the Coroner," he said.