Keen eyed Bunnings staff have been credited with helping foil what could have been Australia’s deadliest home-grown terror attack.

Ahmed Mohamed, 25, Hamza Abbas, 23, and his cousin Abdullah Chaarani, 27, were found guilty in the Supreme Court on November 2 of acts in preparation for an attack targeting Melbourne’s busy Federation Square, St Paul’s Cathedral and Flinders Street station in December 2016.

The verdict, made public on Wednesday after legal delays, followed seven days of deliberations in the jury room and eight weeks of evidence including from Hamza’s older brother Ibrahim Abbas, 24, who confessed his involvement to police and pleaded guilty earlier this year.

In details only now available, it has emerged that staff at a Broadmeadows Bunnings store played an integral role in preventing the attack.

It was staff at the Pearcedale Parade store who alerted police after a young man made an unusual purchase in December 2016, Fairfax media reported Thursday.

Mohamed, then aged in his early 20s, bought 700 nail gun cartridges packed with gunpowder and left without making any other purchase.

Staff were so suspicious that one of them followed Mohamed into the Bunnings car park to take down the registration details of his sedan and raise the alarm.

Federal police were already watching Mohamed as he and his co-conspirators plotted to “wage violent jihad” in Melbourne on Christmas Day.

Ahmed Mohamed, Abdullah Chaarani and Hamza Abbas in court. Photo: ABC

The plot was foiled on December 22, 2016 by police who had been listening to their preparations and watching as they carried out reconnaissance at Federation Square.

Reports also emerged on Thursday that ASIO boss Duncan Lewis has highlighted the work of a particular young security analyst in foiling their plan.

His comments were made to military officials in September at a Land Forces conference in Adelaide but couldn’t be reported until now for legal reasons, the ABC reported.

“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,” Mr Lewis reportedly said.

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

During his arrest, Chaarani asked police to “make me a martyr”, officers revealed.

Mohamed and Chaarani laughed and chatted to each other between the individual verdicts this month. Both nodded slowly and looked indifferent as the guilty decision was given.

As they were removed from the dock, Mohamed gave his family a big, cheesy grin, while Hamza gave his a thumbs up.

Police left court carrying two machetes Chaarani and Ibrahim bought in preparation for the attack.

Ibrahim said they were for “chopping to kill” and to slice the necks of disbelievers of their radical Sunni Islam.

The group also had the makings for pipe bombs – sparkler dust, hundreds of match heads and chemicals including hydrogen peroxide – that were intended, as Ibrahim put it, to “wage violent jihad”.

They got the recipe from the infamous al-Qaeda magazine article “How to make a bomb in the kitchen of your mom”.

Ibrahim revealed during the trial that he believed it was “fine for me to kill Australians” because Muslims have been killed in wars involving Australia.

“It’s not hard to kill a person with a machete. It just takes one slice to the neck,” he said in his police interview.

In Hamza’s defence, lawyer Felicity Gerry QC argued he was a “fishbrain” and the “idiot brother” who could not be trusted to know details of the plot.

Hamza joined in December 2016, but plans between Ibrahim, Mohamed and Chaarani had been afoot since at least October.

Mohamed and Chaarani had tried in 2015 to go overseas and fight with Islamic State.

Chaarani said he wanted to “follow the same path” as Hamza and Ibrahim’s cousin Nabil Abbas who, it was revealed during the trial, had died fighting with the terrorist organisation.

Hamza, Mohamed and Chaarani will face a plea hearing before being sentenced.

-with AAP