Australia's Intelligence Organisation has revealed they received a call around two days before the deadly siege, advising them to 'take a look at this man's website'. The caller did not suggest Monis was planning a terrorist attack, had a weapon or that he planned to take any hostages.
The call to the security hotline will be a key component of the review ordered by Prime Minister Tony Abbott to establish more clarity about the terrifying incident, reports the Daily Telegraph.
It was reported that ASIO examined Monis's website, which features rambling posts about terrorism fuelled protests in Martin Place, as a result of the call.
Monis had numerous social media websites, including a Twitter and Facebook account-the latter of which had 14,000 'likes'-which he used to preach extremist jihadist views.
It comes after the revelation that Monis may have initially planned to attack the offices of Channel Seven in a terrorist attack.
In 2009, Channel Seven's Today Tonight show exposed Monis for sending abusive 'condolence' letters to the families of Australian soldiers killed in Afghanistan.
The program, which labelled Monis a 'Fake Sheik', led to the conviction of he and wife Amirah Droudis in the High Court over the letters.
On several occasions after the program aired, Monis protested on the steps outside the Seven Studio with pro-Islamic leaflets.
In the early hours of Monday morning, it's understood the gunman walked around Martin Place before entering the Lindt Cafe and sitting for up to an hour before taking customers and staff hostage.
One of Monis' former lawyers encountered the man in the cafe by chance on Monday morning and described his behaviour as distinctively calm.
'He was cool as a cucumber, not agitated, not scoping the place out, not looking over his shoulder,' said the lawyer. 'He kept asking, 'Why are you here?'. I think he was genuinely surprised to see me there.'
The evidence comes after reports that the siege gunman told police in 2008 he planned terrorism-related 'protests' in Martin Place just metres from the café where he took 18 hostages this week.
Man Haron Monis also wrote letters to Qantas's chief executive in 2009 suggesting he had information about sabotage at the airline that would lead to mass casualties.
Prime Minister Tony Abbott has launched a major investigation into why security services allowed Monis to drop off a terrorism watch list despite numerous examples of extremist views and behaviour, reports Sydney Morning Herald.
