In the bright sunshine on the steps outside the convention centre, a gaunt, bearded figure jabs his finger into the air and chants: ''Christopher Hitchens, burn in hell!''

The small group of men clustered around him repeat the slogan as they wave signs describing atheism as a cancer and Islam as its cure. They appear to relish the abuse rained down on them from the large crowd surrounding them.

The protest outside this year's Global Atheist Convention at the Melbourne Convention and Exhibition Centre - captured on video and posted on YouTube - was the Australian public's first glimpse of Harun Mehicevic and his band of devoted followers. But the next time the public spotlight fell on him, it would be in far more dramatic circumstances.

When federal and state police swarmed into properties across Melbourne 12 days ago, searching for evidence of terror-related offences, the al-Furqan Islamic bookstore in Springvale South was quickly identified as a common link between all of those targeted.

People within Melbourne's Islamic community then named Bosnian-born Mehicevic - also known as Abu Talha - as the spiritual leader of a deeply conservative group of men who congregate at the bookstore.

In the days after the raids, The Age managed to track down a number of people connected with al-Furqan and question them about their beliefs and activities. Some of Mehicevic's followers have also taken to social media to deny allegations of terror-related activities and criticise police over the raids.

But throughout all this, Mehicevic has remained a shadowy figure. The Age revealed that he was in Bosnia when the raids took place, and that he had given a statement to Bosnian police. Because Australian police had not issued a warrant for his arrest, he was allowed to walk free.

With one of his followers, 23-year-old Adnan Karabegovic, languishing in custody after being charged with collecting documents in connection with the preparation of a terrorist act, two questions remain: Who is Harun Mehicevic? And does he pose a threat to our community?

Sources have told The Age that he came to Australia from Bosnia as a young adult in the mid-1990s, and that he has a Pakistani-born wife and six children. They say he studied arts at Deakin University and possibly gained a diploma in teaching.

Somewhere along the way, Mehicevic turned to a conservative and purist form of Islam known Salafism. He became a follower of hardline Melbourne cleric Sheikh Mohammed Omran, and associated with Abdul Nacer Benbrika, who is serving a 15-year jail term for planning a terrorist attack in Melbourne in 2005. When Benbrika split from Omran, Mehicevic remained loyal to the senior cleric.

However, the relationship between Omran and Mehicevic began to sour last year when the Bosnian assumed powers some said he was not entitled or qualified to wield. Sources say he began to issue fatwas, or judgments, against people he accused of not being true Muslims, and began to select spouses for people and recommend divorces.

In a power struggle, Mehicevic and his followers wrested control of the al-Furqan centre from Omran's organisation, and effectively banished Omran's followers from the centre.

Sources within the Islamic community have described him as a ''cult leader'' and ''charismatic but totally delusional''. They say he has gathered a multi-ethnic group of 20 to 30 young men around him, and they are fiercely loyal to him.

''He tells them exactly what they want to hear,'' a source said.

''Hate the kuffar [unbelievers]; hate the system.''

Some families were so concerned about the hold Mehicevic had over their children they moved overseas to get them away from his influence.

Many of those standing around Mehicevic in the video taken at the atheist convention are believed to be from al-Furqan. While they engage in angry exchanges with the atheists confronting them, Mehicevic remains aloof, only occasionally chanting or talking intently to those around him.

Although some of them are of Bosnian origin, they wear clothes of Pakistani or even Saudi Arabian appearance as a way of proclaiming their hardline beliefs.

Some who have listened to Mehicevic preach say he has advocated violent struggle against Western troops in Iraq and Afghanistan, and has gone as far as hailing suicide bombings aimed at civilians in other countries. However, they say they have never heard him advocate terrorist acts in Australia, and question whether he would jeopardise his hold over al-Furqan and his comfortable existence by doing so.

The Age has been told the raids - coupled with the unmasking of an alleged ASIO informer within al-Furqan last month - could drive Mehicevic's followers closer together, and make them more secretive.

There has also been speculation the raids were triggered by the discovery of the alleged informer - who has strenuously denied the allegations, despite the discovery of text messages apparently exchanged by him and his ASIO handler - rather than concrete evidence of terror plans.

- The Age