CANBERRA, Nov. 15 (Xinhua) -- A rookie Australian Security Intelligence Organisation (ASIO) female officer was key in stopping maybe the largest terrorist attack in the nation's history, it has been revealed.

The Supreme Court of Australia on Wednesday evening lifted a suppression order on the trials of Abdullah Chaarani, 27, Ahmed Mohamed, 25, and Hamza Abbas, 23, revealing that the three men were found guilty of plotting a major terror attack on iconic Melbourne landmarks.

A fourth man, ringleader Ibrahim Abbas, pleaded guilty to all charges in February and gave evidence against his brother, Hamza, and cousin, Abdullah.

Chaarani, Mohamed and Abbas face lifetime prison sentences after the court heard that the four men purchased pre-cursors for explosives as well as machetes as part of their planned attack on Melbourne Central Business District (CBD) in December 2016.

They planned to use knives, explosives, vehicles and suicide vests to attack large crowds gathered in the city ahead of Christmas.

Duncan Lewis, director general of ASIO, has detailed how a female officer who had been a member of Australia's top spy agency for only a few days noticed the men "performing in an unusual way" leading up to Christmas in 2016.

"The Christmas crowds were gathering and we, as the result of the exertions of a young ASIO officer, a young woman who'd been with us for about five minutes, one of our analysts, had noticed a group of young men performing in an unusual way and going to a chemist's shop very late at night," Lewis said.

"They were in fact picking up the precursors for explosives. That was all the lead we needed."

Lewis made the comments during a speech to military officials at the Land Forces conference in Adelaide in September but the information could not be made public until the trial and any appeals were concluded.

The four men, all of who were born in Australia, were arrested on Dec. 22, two days after they carried out a reconnaissance mission in the CBD, and charged with conspiring to carry out a terrorist attack.

Evidence presented by the prosecution during the trial revealed that the men were inspired by Islamic State (IS). Enditem