Australian Federal Police Commissioner Andrew Colvin emphatically rejected during a Senate estimates hearing on Thursday night claims the sword was plastic.

"Senator I'm pleased that you've asked this question," he told Liberal Democrat Senator David Leyonhjelm.

"I can absolutely guarantee the committee it was not a plastic sword. It was a metal sword," Mr Colvin said. "Categorically I can say that it was a metal sword."

The sword was seized as evidence by federal and NSW police when they searched a Marsfield home at dawn on September 18 as part of the major Operation Appleby counter-terrorism raids.

One man, 22-year-old Omarjan Azari, was charged after the raids across Sydney in connection to an alleged plot to seize a member of the public and kill them while filming the murder.

But another young man who was arrested at the home where the sword was found, Mustafa Dirani, 21, afterwards insisted the sword was merely a plastic decoration, commonly found in Shiite households.

Mr Dirani was held by police but later released without charge. He has said his family is Shiite, not Sunni, which is the Muslim sect associated with the Islamic State group to which the alleged mastermind behind the terrorism plot, Mohamed Ali Baryalei, is supposed to belong.

Earlier this month, AFP Assistant Commissioner Neil Gaughan told ABC's Q&A that the sword was not plastic, and that it was a "legitimate weapon".

Mr Colvin said the sword was inscribed with Arabic writing but was unable to say immediately whether it was Sunni or Shia.

He said his officers were trained to understand the Islamic religion but could not say whether they could distinguish Sunni religious script from Shiite script. He added that it was "irrelevant" because police did not base their operations on which sect a suspect belonged to.

"I wouldn't want my officers to make a predetermined judgement based on whether they thought somebody was Sunni or Shia."

He said the sword was still being held as evidence, along with other material. Police were yet to make a judgment as to whether it could be returned.