System let us down with Sydney siege "monster": Australian PM

Armed with a pump-action shotgun, Iranian-born self-styled cleric Man Haron Monis took 17 people hostage in Sydney's Lindt Chocolate Cafe on December 15.

Some 17 hours later he shot dead cafe manager Tori Johnson, 34, prompting police to storm the building and kill him. Another hostage died in the crossfire.

In the aftermath of the siege which shocked the nation it emerged that Monis, who had been living in Australia since the 1990s, was on bail at the time for a string of charges, had no gun licence and had long been on the radar of security agencies.

"Plainly, in their totality, the system has let us down," Abbott told reporters in Sydney in releasing the government's first review into the incident.

"Plainly, this monster should not have been in our community. He shouldn't have been allowed into the country. He shouldn't have been out on bail. He shouldn't have been with a gun. And he shouldn't have become radicalised."

Abbott said the review found that decisions were made about Monis at various levels -- beginning with the immigration department but extending to mental health authorities, the police and intelligence agencies -- which were justifiable under the circumstances.

"We don't believe that at any particular decision-making point, grievous errors were made, but the totality of decision-making let this monster loose in our community," he said.

Abbott, who on Monday will deliver a national security address, said when it came to the tipping point in balancing the protection of the individual against the safety of the community, "precisely where we draw the line in the era of terrorism will have to be reconsidered and the line may have to be redrawn".

The prime minister said that in Monis's case, authorities had realised fairly quickly that he had lied on his initial application to come to Australia, as he flagged more checks and scrutiny on the pathway to citizenship.

18 calls to security hotline

The review revealed that 18 calls were made to an Australian national security hotline about Monis in the days before he carried out the siege. The calls between December 9 and 12 were all concerned about offensive material on his Facebook page.

"None of the calls related to any intentions or statements regarding a pending attack -- imminent or otherwise," the review said, adding that all were all considered by intelligence and police authorities.

"On the basis of the information available at the time, he fell well outside the threshold to be included in the 400 highest priority counter-terrorism investigations," the review said.

"He was only one of several thousand people of potential security concern."

In a statement, Abbott and New South Wales state Premier Mike Baird said the review found "there were no major failings of intelligence or process in the lead-up to the siege".

Right up until the siege, intelligence and law enforcement agencies had "never found any information to indicate Monis had the intent or desire to commit a terrorist act".

But the review found that in the last months of his life, Monis had apparently become inspired by the Islamic State group and had rapidly become radicalised.

Australia raised its threat level to high in September and carried out a series of counter-terrorism raids following the departure of some of its nationals to Iraq and Syria to fight with Islamic State and other jihadist groups.

"The Martin Place murderer right up to the very end was not specifically advocating violence against Australians," Abbott said.