"It lasted four years to collect evidence on Manteqi's [Monis'] identification documents and we reported this to the Australian police but since Australia has no extradition treaty with Iran, they didn't extradite him," General Moghaddam told the Mehr News Agency.

General Moghaddam said Iranian police spent four years collecting evidence against Monis, before seeking his extradition to Iran from Australia.

General Moghaddam told the Iranian Mehr News Agency that Monis posed as a cleric at the time to gain political asylum. Earlier Monis had been the manager of a travel agency in Iran, authorities there said.

Once the Australian government granted asylum to Monis, it would have been in breach of the Refugee Convention to send him back to Iran, unless it was proved that he had obtained that status through fraud.

The government would also have been highly unlikely to send him back while his asylum application was pending, though it might have had to consider evidence provided by Iran of alleged crimes carried out by Monis in his native country.

Monis, 50, was shot dead when police stormed into the Lindt Chocolat Cafe just after 2am on Tuesday, more than 16 hours after he entered the cafe armed with a gun and held 17 customers and staff hostage.

At the time, Monis was before the courts on two separate and serious matters: more than 40 sexual assault charges involving seven alleged victims and as an accessory to the murder of his former wife.

The NSW government has called for an investigation into why Monis "slipped through the cracks" of the judicial system and was released from custody.