Law experts express detention concern

Australian Federal Police insist the detention without charge of an 18-year-old connected to police employee Curtis Cheng's murder is necessary to sift through evidence from Tuesday's pre-dawn Sydney raids.

The 18-year-old man, who cannot be named, will be held for 100 additional hours (four days) after investigators were granted judicial approval on Thursday to increase the length of time he can be detained.

These hours are consecutive and do not permit further interrogation.

"This recognises that terrorism investigations can be complex and that there may be legitimate reasons for extended periods of detention for suspects," said an AFP spokesperson.

"At this point in time, the presumption of innocence still applies."

Legal experts have nevertheless questioned the implications of the move, arguing it undermines the rule of law to keep individuals without charge for so long.

Greg Barns from the Australian Lawyers Alliance said the maintenance of due process is equally as important as community safety.

"In a civilised society you do not detain people without charge, and you have to ask the question: why were these people swept off the streets and taken into custody in any event if they weren't charged?" asked Mr Barns.

"Even in the most serious investigations like murder, people progress through the system relatively quickly and are charged.

"To keep a person in detention without charging them and without telling the court a great deal about why they want to keep that person is very dangerous."

Human Rights Commissioner Gillian Triggs was reassured by the court's supervision over the detention but said the secrecy of the judiciary's decision was problematic.

"Providing these matters are regularly supervised by judges under the piece of relevant legislation, we think that balance is being properly met," Professor Triggs said.

"But we are always concerned about closed processes because it's very hard to ensure the proper checks and balances.

"The more transparent the process, the easier it is to know that fine line is being met."

Mr Barns disputed this view, saying magistrates are forced to determine applications on less than optimal information.

"The (detention) application has to set out why police want it but can give a whole lot of exemptions on what they have to tell the magistrate about," he said.

"You get a situation where a person can be held without charge, effectively incommunicado, and yet magistrates are being forced to make decisions on less than all the available information.

"This sort of 'dead time' idea is unique to terrorism cases."

Mr Barns said this form of apprehension could contribute in its own way to radicalisation.

"It certainly doesn't help when your laws are antithetical to fairness," he said.