A Sydney-born terrorism plot to place a bomb on a passenger plane was dangerously close to being carried out before it was unwittingly thwarted at an airline check-in counter.
New details about the attempt to bring down the commercial flight out of Sydney provides a chilling insight into how close Islamic State-inspired terrorists allegedly came to executing the mass-casualty attack.
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One released without charge over plane terror plot
Police release one of the four men they arrested, without charge, over the terror plot to blow up a plane.
Fairfax Media understands an improvised device reached Sydney Airport's international terminal after a passenger packed it inside a piece of luggage.
The passenger was queried about the weight of the luggage at the check-in counter and learnt it was too heavy. The bag was never checked in or carried on the plane.
Authorities uncovered this after Khaled Merhi, Khaled Khayat and Mahmoud Khayat were arrested in counter-terrorism raids across Sydney on Saturday evening.
They were detained over an alleged and pending plot to smuggle an improvised explosive device on to an Etihad flight departing Sydney for Abu Dhabi.
As the men spent their fifth day in custody, Prime Minister Malcolm Turnbull confirmed on Thursday that charges would be laid after police uncovered "very substantial evidence".
"The [Australian] Federal Police Commissioner, Andrew Colvin, has advised me that the investigation efforts are proceeding very successfully in terms of the gathering of evidence," he said.
![Security at Sydney Airport has been ramped up.](http://web.archive.org./web/20170803083031im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/l/q/l/1/image.related.articleLeadwide.620x349.gxodlz.png/1501741637184.jpg)
"And that I should expect, and Australians should expect, charges to be laid in due course."
Abdul Merhi, 50, Khaled Merhi's brother, who was also arrested, walked from police custody without charge on Tuesday night.
![Khaled Khayat, pictured at Sydney Airport in 2014, is one of the men arrested.](http://web.archive.org./web/20170803083031im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/m/1/t/3/image.related.articleLeadwide.620x349.gxodlz.png/1501741637184.jpg)
For the past several days, police have been scouring through the Surry Hills, Lakemba, Punchbowl and Wiley Park homes of the four men, who are related through marriage.
A meat mincer, which would either explode or disperse deadly gas, was the suspected weapon. It is understood it was among the items seized from the Surry Hills terrace.
![NSW Police Commissioner Mick Fuller.](http://web.archive.org./web/20170803083031im_/https://www.fairfaxstatic.com.au/content/dam/images/g/w/e/1/4/6/image.related.articleLeadwide.620x349.gxodlz.png/1501741637184.jpg)
Since police turned their focus to the alleged plotters last week, investigators uncovered information about the alleged earlier attempt that got as far as the airport terminal.
It is unclear when the close call occurred, although it was before police launched their investigation into the Sydney men last week.
![Police examine items outside a Lakemba unit on Monday as part of their investigation into an alleged terrorism plot.](http://web.archive.org./web/20170803083031im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/m/5/9/g/image.related.articleLeadwide.620x349.gxodlz.png/1501741637184.jpg)
Multiple sources have confirmed the earlier attempt but said that, even if the device did make it past the airline check-in, it might have been detected in a security screening.
NSW Police Commissioner Mick Fuller said on Thursday there had been a lot of speculation about what the alleged attack entailed, but added that police stopped what could had been a "horrible crime".
![Police at the scene of the terrorism raid in Surry Hills](http://web.archive.org./web/20170803083031im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/l/h/c/0/image.related.articleLeadwide.620x349.gxodlz.png/1501741637184.jpg)
"Terrorism is very different to other crimes; you cannot wait until you have the perfect brief, you cannot wait until you have all the pieces of the puzzle because you cannot afford to let the criminal act happen," he said.
"When we go early to protect the community, it gives us an opportunity to make sure we gather all the necessary evidence.
![The scene of a terrorism raid in Surry Hills.](http://web.archive.org./web/20170803083031im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/l/h/o/r/image.related.articleLeadwide.620x349.gxodlz.png/1501741637184.jpg)
"I think, in the coming days as this matter progresses, and in my opinion people will be charged and the facts are tendered, you will understand about the police operation more holistically."
Security measures at Australia's major airports were heightened last week after police received information about the alleged bomb threat.
![Khaled Khayat was arrested in Surry Hills over the terrorist bomb plot.](http://web.archive.org./web/20170803083031im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/m/h/m/v/image.related.articleLeadwide.620x349.gxodlz.png/1501741637184.jpg)
The move prompted lengthy passenger queues that snaked outside terminal doors as travellers were urged to arrive hours before their flights.
However, following advice from ASIO that there was no longer an active threat to the aviation industry, some security measures would be eased, Mr Turnbull said.
![Five properties in Surry Hills, Punchbowl, Wiley Park and Lakemba were raided as part of a counter-terrorism operation ...](http://web.archive.org./web/20170803083031im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/l/u/r/x/image.related.articleLeadNarrow.300x0.gxodlz.png/1501741637184.jpg)
People should follow the directions of their airline, he added.
"There will be continued enhanced security measures. Some of them will be visible to travellers, some of them will not," he said.
It is understood that British and US spies fed information about the alleged bomb plot to their Australian counterparts.
That came after communication was intercepted between members of the alleged Sydney terrorist cell and Islamic State operatives in Syria.
Police then launched the dramatic counter-terrorism raids on Saturday evening.
Investigators are now looking closely at the background and associations of those involved, who were little more than a blip on the terrorism radar before last week.
Khaled and Abdul Merhi are understood to be related to Ahmed Merhi, who was once viewed as an active recruiter for IS in Syria, where he has been based since 2014.
However Abdul Merhi's lawyer, Moustafa Kheir, said it was "unfathomable" his client would be associated with such a terrorist plot.
"A lot of information was divulged, including his identity," he said on Wednesday.
"That's caused a lot of damage to him. We want to review all the information police had and what basis they had to do what they did."
Abu Dhabi-based Etihad Airways, the group's alleged target, issued a statement on Tuesday saying it was helping police with the investigation.