Man arrested in Sydney terror plot released without charge

A group of men accused of plotting to bring down an international flight may have been building a bomb with 'mother of satan' gas, which was used in the Manchester Arena attack, a terror expert has claimed.

The new details of the alleged plot comes as one of the suspects was released without charge on Wednesday morning.

The remaining three men will remain in police custody, an Australian Federal Police spokesman told Daily Mail Australia. 

The alleged conspiracy to bring down a passenger plane with a gas bomb was as close as Australia has come to a major terror attack, a source has revealed. The men (one pictured being led away by police) were arrested in dramatic raids in Sydney on Saturday

The alleged conspiracy to bring down a passenger plane with a gas bomb was as close as Australia has come to a major terror attack, a source has revealed. The men (one pictured being led away by police) were arrested in dramatic raids in Sydney on Saturday

Khaled Khayat, pictured in a Canterbury-Bankstown Bulldogs jersey, is one of the Lebanese-Australian men who were arrested

Khaled Khayat, pictured in a Canterbury-Bankstown Bulldogs jersey, is one of the Lebanese-Australian men who were arrested

Two of the accused are reportedly related to infamous jihadist Ahmed Merhi (pictured), who travelled to Syria in 2014

Two of the accused are reportedly related to infamous jihadist Ahmed Merhi (pictured), who travelled to Syria in 2014

The alleged plot was 'fairly well along' when authorities swooped on Saturday, US officials believe.

News agency Reuters on Tuesday cited two US officials familiar with the arrests as also saying the Australian investigation wasn't a sting operation but the result of the detection of a developing plot. 

Etihad has confirmed it's helping authorities.

'The Etihad Airways aviation security team is assisting the AFP with its investigation and the matter is ongoing,' the airline said in a statement.

'Etihad is complying fully with the enhanced security measures at airports in Australia and monitoring the situation closely.'

Investigators on Monday found a Qantas release slip relating to a Sydney to Jakarta flight near one of the raided Sydney properties but AAP understands the plot did not involve Qantas or the Qantas Group.

Authorities have refused to officially confirm any details about what they've found after rifling through properties in four Sydney suburbs.

However, one theory is the plot involved the use of a meat grinder to conceal a home-made device. 

New South Wales Police officers arrive at a crime scene in Surry Hills in Sydney on Monday

New South Wales Police officers arrive at a crime scene in Surry Hills in Sydney on Monday

One of the accused is pictured with a bandaged head following his arrest on Saturday night 

One of the accused is pictured with a bandaged head following his arrest on Saturday night 

The target of the alleged terror plot was an Etihad flight from Sydney to Abu Dhabi with up to 500 passengers and crew on board (stock image)

The target of the alleged terror plot was an Etihad flight from Sydney to Abu Dhabi with up to 500 passengers and crew on board (stock image)

Deakin University terror expert Greg Barton suggests the plan may have centred around acetone peroxide - or TATP - the same chemical used in the Manchester Arena bombing in May and the 2015 Paris attacks.

Referred to as the 'mother of Satan' because it can kill those handling it, TATP is unstable but powerful and would not give off 'tell-tale' chemicals picked up by airport swab tests, Prof Barton told AAP.

'That makes it a candidate for using in this sort of attack.'

TATP, which needs a pressure vessel to be packed in, could be placed in a grinder so it was opaque through an X-ray machine and appeared innocuous upon visual inspection.

'It might just pass (security),' Prof Barton said.

'That, I'm guessing, was their plan.' 

The group had allegedly planned to put toxic gas in a meat mincer which could have exploded or poisoned passengers on a packed commercial jet. Pictured, a policeman at the scene of one of the Sydney raids

The group had allegedly planned to put toxic gas in a meat mincer which could have exploded or poisoned passengers on a packed commercial jet. Pictured, a policeman at the scene of one of the Sydney raids

Justice Minister Michael Keenan (pictured right alongside Prime Minister Malcolm Turnbull) told would not comment on the IS links, but stressed the significance of the attack if it had taken place

Justice Minister Michael Keenan (pictured right alongside Prime Minister Malcolm Turnbull) told would not comment on the IS links, but stressed the significance of the attack if it had taken place

NSW Police and forensic officers at the scene of a counter-terrorism raid on a property in Cleveland Street in Surry Hills

NSW Police and forensic officers at the scene of a counter-terrorism raid on a property in Cleveland Street in Surry Hills

Prof Barton

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