'Idiot' Defence In Victorian Terror Plot Case

Hamza Abbas could not be trusted to know the details of an alleged Christmas Day Melbourne terror plot, and jurors deciding his involvement might judge him the "idiot brother" rather than complicit, his lawyer says.

The 23-year-old is on trial in the Supreme Court with his cousin Abdullah Chaarani, 27, and Ahmed Mohamed, 25, charged with conspiring to prepare and plan an attack on Federations Square, Flinders Street Station and St Paul's Cathedral two years ago.

His older brother, 24-year-old Ibrahim Abbas, has already pleaded guilty to the same charge.

But Felicity Gerry QC says common sense dictates that siblings do not always agree and while Ibrahim was radicalised after years of jihad research, there was no evidence Hamza had similar radical interests.

"He is simply not a jihadi. He is just a good Muslim," she said on Monday.

In closing submissions after seven weeks of evidence, Gerry said Hamza had learning difficulties.

Abdullah Chaarani, Ahmed Mohamed and Hamza Abbas, Court Sketch

She reminded jurors of evidence from his sister Nabilla Abbas, who said he was once sent to buy milk and had to call home twice to be reminded what to do.

"If you send Hamza for a Ramset cartridge he'll come back with plant pots," Gerry said.

"There's no point telling him the purpose or detail, he can't be trusted."

Jurors could even conclude "taking an idiot brother was good cover", she said.

Gerry raised Ibrahim's suggestion he would strap a vest on Hamza on the day of an attack, noting "strap them and drop them" would be easier than explaining the plot.

Crown prosecutor Nick Papas QC earlier said it was obvious the trio wanted to "wage violent jihad" against non-believers.

Hamza is accused of joining the plot in December, while it's alleged Mohamed and Chaarani's plans were on foot by late October 2016.

Hamza Abbas. Image: Facebook

Papas played an extremist video found on Chaarani's phone showing pictures Federation Square, St Paul's Cathedral and the Yarra River, calling others to "come to martyrdom".

He also showed a CCTV clip of the accused and Ibrahim meeting at Federation Square.

"The Crown says they're talking about this as a great place to cause lots of mayhem and injuries, lots of innocent people to be killed, the more the better," Papas said of the CCTV.

He said Ibrahim's claim in court that he had suggested it as a suitable location for an attack during a spontaneous trip was "ridiculous".

Mohamed is alleged to have saved an al-Qaeda magazine article "How to make a bomb in the kitchen of your mom" in October, shortly before Chaarani researched sparkler explosives.

Mohamed and Ibrahim also bought materials including light globes, pipes and Ramset cartridges, the prosecution argues.

There were also three trips to Clonbinane, where it's alleged explosive devices were tested.

When the bombs failed, prosecutors say the men moved on to a new method using hydrogen peroxide, which Hamza and Mohamed were seen buying.