A Sydney man arrested over a terror conspiracy to bring down a plane and then released without charge is shocked to have been associated with the allegations, his lawyer says.

Abdul Merhi, 50, was one of four men arrested on Saturday when five Sydney properties were raided by NSW and Australian Federal Police.

Authorities became aware of an alleged plot to “bring down” a plane using a home-made device and detained the men without charge under terror legislation.

Mr Merhi was released about 7pm Tuesday.

His solicitor, Moustafa Kheir, said his client had endured 3½ days of intense questioning, with the arrest and allegations causing “a lot of damage to him”.

Mr Merhi said he had felt like he was “in a movie” when he was told of the allegations of a plot to bring down a plane, while Mr Kheir said the experience had proved very stressful to his client.

“There’s a lot of stress associated there, and not knowing, and he was shocked that he was being questioned,” Mr Kheir said.

“It’s just unfathomable that he would be associated with anything like this.”

Mr Merhi’s brother Khaled Merhi and relatives Khaled Khayat and Mahmoud Khayat remain in custody and can detained until Sunday evening under the terror legislation.

Khaled Khayat (L) and Mahmoud Khayat remain in police custody. Photo: Supplied

Mr Kheir said he would review the actions of police.

“A lot of information was divulged, including his identity,” he said.
“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.”

Mr Merhi’s family was also in shock and his life had been “turned upside down”, Mr Kheir added.

“He just wants to go back to as normal life as possible now.”

Police have spent days rifling through properties in Lakemba, Wiley Park, Punchbowl and Surry Hills in the search for evidence.

“This investigation remains ongoing, and further information will be provided at an appropriate time,” a joint statement from the AFP and NSW Police said on Wednesday.

While little has been officially confirmed about the allegations against the men, one theory is that the plan involved hiding a device inside a meat grinder.

Professor Greg Barton, a terrorism expert at Deakin University, said the suspects may have been directed by handlers in Syria.

“My speculative guess is they were probably trained in how to prepare TATP,” he told AAP.

The chemical TATP, which was used in the Manchester Arena bombing in May and also in Paris in the 2015 attacks, is unstable but can be powerful when placed in a pressure vessel.

Prof Barton said the conspiracy was “clearly the most sophisticated terror plot” Australia had ever seen, but it likely would have failed.

Etihad Airways has confirmed it was helping Australian authorities with the investigation, amid reports the arrests were made after a tip-off from foreign intelligence services.

– with AAP