Saudi Arabian security services captured Perth man Shayden Thorne in a raid on the hideout of an alleged extremist group they accuse of planning to join mujahideen fighters in Afghanistan.
The man's younger brother, Junaid, also an Australian, was arrested in Riyadh more than a year later, filming on his mobile phone while protesters jeered outside a mosque in the Saudi capital.
Experts warned Shayden Thorne, 25, could face the death penalty if convicted of terrorism charges in Riyadh Special Criminal Court, where he faces trial almost 18 months after his arrest in November 2011.
His brother, Junaid Thorne, 23, was freed in February after two months in jail, having been arrested at a protest about the treatment of prisoners. Junaid has since been asked to surrender his passport after questioning by Saudi officials last month and cannot leave the kingdom, even though his residency permit has expired.
Family in Australia fear for the safety of the men and their mother has accused the Foreign Affairs department of not doing enough to have them returned to Australia.
But Foreign Minister Bob Carr said Australian diplomats have made at least 50 representations on behalf of the brothers, including a message by Senator Carr to his Saudi counterpart. ''We want it resolved faster. It's been going on for too long,'' Senator Carr said.
The mother, who did not want to be named, told Perth radio Junaid took more than a month to tell her Shayden had been imprisoned.
''I thought it was a bit strange and I kept trying to call him, I wasn't getting through and his brother at the time, he knew what had happened but he thought he better not tell me because I would, you know, worry. He thought that I would freak out, which is the truth,'' she said.
''It's well known over there that when these Saudi secret police take somebody, you just never know if you are going to see them again. He didn't want to tell me that was exactly what happened.''
Saudi Arabia ranks among the top five countries imposing the death penalty - the bulk carried out by public beheading.
A spokeswoman for Senator Carr confirmed the death penalty is the maximum sentence for terrorism cases in Saudi Arabia but said: ''There has been no indication from Saudi contacts that it might be a prospect in this case.''
Prison sentences were given in an unrelated case last month to eight men accused of plotting attacks on an Saudi oil refinery.
The Thorne brothers have lived in Saudi Arabia for 12 years. Australian officials have sought co-operation from Saudi officials to allow Shayden more access to sunlight and exercise during his nearly 18 months in prison.
He last appeared in court four days ago and Murdoch University international studies specialist Rajat Ganguly warned that if found guilty of terrorism charges he was likely to face the death penalty.
Shayden has accepted a state-appointed lawyer as counsel.
He was arrested after Saudi security services raided a compound where a group of alleged extremists had been gathering.
The group are accused of accessing mujahideen websites linked to the Afghanistan war and planning fight there.
Islamist extremists have long railed against the rule of the Saudi royal family as oppressive and corrupt.
The mother, who moved back to Australia last year, dismissed allegations Shayden was in possession of a laptop with terrorist related material on it. She said the laptop was borrowed from the mosque he attended. ''That same laptop, he used to bring it around to the house because we had no TV … He had all kinds of movies that he put on that laptop,'' she said.
The next hearing is expected within a month.