It has been a long road for everyone involved in the Sydney siege and the events that led to the December 2014 tragedy.

Last night, Four Corners revealed the full extent of the systemic oversights and bureaucratic bungles that meant Man Haron Monis, the Lindt Cafe gunman, was at large.

The revelations come just a day before NSW State Coroner Michael Barnes prepares to hand down his findings into the coronial inquest.

The Lindt Cafe inquest is one of the longest and most complex in the state's history, with 23 weeks of public hearings and hundreds of individual pieces of evidence.

It is not yet known what findings or recommendations Mr Barnes will make.

But based on the evidence which played out in the inquest, he is likely to be critical of a number of factors.

The national security risk

Gunman Monis was well known to NSW Police, the Australian Federal Police (AFP) and the Australian Security and Intelligence Organisation (ASIO) when he took 18 people hostage in December 2014.

The self-styled sheikh arrived in Australia from Iran in 1996 seeking asylum from persecution. He was granted citizenship in 2004.

He gained a reputation as a "serial pest" when he repeatedly called ASIO's public information line to provide it with "information" relating to the Sydney Olympics and the 2005 London bombings.

The inquest heard Monis was the subject of 18 separate tip-offs to the National Security Hotline after he posted statements on his Facebook page pledging allegiance to the "caliph of the Muslims" in the days before the siege.

ASIO analysed the posts and concluded: "They did not indicate a desire or intent to engage in terrorism."

NSW Police last month established the Fixated Persons Investigations Unit — a team of specialist detectives and mental health experts set up to investigate people driven by extreme political, religious or ideological beliefs who make threats of violence.

The unit has been set up as a direct response to the failure of police to recognise the threat posed by Monis.

Despite this, the coroner may find that state and federal agencies should have been aware that Monis was radicalising and that he posed a risk to public safety.

The decision to release Monis on bail

Man Haron Monis, who held 17 people hostage in the Lindt cafe in Sydney’s Martin Place. ( AAP )

The inquest heard Monis was allowed to walk free on bail on three separate occasions when he fronted court on serious criminal charges in the 12 months before the siege:

Monis was charged with being an accessory to his ex-wife's murder in November 2013 but was granted bail in December, much to the surprise of his solicitor.

Monis was charged with being an accessory to his ex-wife's murder in November 2013 but was granted bail in December, much to the surprise of his solicitor. In 2014, Monis was charged with 43 counts of sexual assault against women at his "spiritual healing" in western Sydney in the early 2000s. He was released on bail thanks to a controversial softening of the NSW bail laws, which were later reversed.

In 2014, Monis was charged with 43 counts of sexual assault against women at his "spiritual healing" in western Sydney in the early 2000s. He was released on bail thanks to a controversial softening of the NSW bail laws, which were later reversed. Detectives from the Sex Crimes Squad pleaded with public prosecutors to have his bail revoked, but they were told there was "no grounds" to have him taken into custody.

The inquest also heard Monis breached his bail on Commonwealth charges of sending letters to the families of soldiers killed in Afghanistan, but NSW prosecutors were unaware of those offences.

The coroner, Mr Barnes, may be highly critical of the mistakes and oversights of solicitors working within the Office of the Director of Public Prosecutions that allowed Monis to remain on bail.

The 'trigger' for police to storm cafe

Police raise their weapons during the siege in Martin Place. ( AAP: Dan Himbrechts )

The inquest heard the senior police commanders in charge during the 17-hour siege did not formally agree on a "trigger" for an Emergency Action (EA) to storm the cafe.

It was only once they were giving evidence that several commanders said the trigger was the "death or serious injury of a hostage" or "imminent" death or serious injury.

The Police Forward Commander, who cannot be identified, told the inquest he did not send police into the cafe until a hostage was killed because he believed the risk was too great.

"They have family and children, too; they were going in to face a man with a bomb," he told the inquest.

Several tactical police told the inquest a Deliberate Action (DA) plan for a pre-emptive strike should have been approved so they could have the option "in their back pocket".

But the inquest heard the Police Operations Commanders, assistant commissioners Mark Murdoch and Mark Jenkins, never approved or authorised such a plan.

The coroner may make recommendations for police to improve their decision-making processes and set formal "triggers" for EAs and DAs when they respond to high risk incidents.

'Contain and negotiate' strategy

There has also been criticism of the "contain and negotiate" strategy police used to manage the Lindt Cafe siege.

Senior officers have told the inquest it was the best strategy to bring about a peaceful resolution, but others have slammed it, saying Monis never intended to live through the siege.

NSW Police has since introduced its Active Armed Offender policy, in which officers would abandon "contain and negotiate" in favour of hunting down and shooting terrorists or armed people who are actively harming members of the public.

The policy is a response to the changing nature of terrorist attacks overseas, but senior police concede the Lindt Cafe siege would not have met the threshold for the Active Armed Offender policy.

The coroner may acknowledge the risks frontline police took when they stormed the Lindt Cafe in the early hours of December 16, 2014.

The failure to share intelligence and resources

This is an area where Mr Barnes could be highly critical; the authorities had an abundance of information to suggest Monis was violent and had become radicalised by the ideology of the Islamic State group.

Much of that information was simply not passed to the police who needed it most.

NSW detectives, the AFP and ASIO all had extensive files on Monis, but very little intelligence made its way to frontline commanders during the siege.

Homicide detective Melanie Staples recognised Monis from live TV footage of the siege just before midday and alerted her commanders.

She prepared a brief of information on Monis, which included his criminal charges, a psychological profile and details of his violent nature.

But the inquest heard that brief did not reach frontline commanders, and it would be another three hours before they knew his identity.

The inquest also heard the AFP had two intelligence reports assessing the backpack "bomb" Monis claimed he was wearing, but those reports were never shared with NSW Police.

The feared existence of a backpack bomb, and the possibility it had a "dead man's switch" that would detonate if Monis was killed, was the primary reason police believed it was too dangerous to pre-emptively storm the cafe.

Faulty equipment and stretched resources

The inquest heard frontline police were dogged by faulty radio communications and computers, which meant crucial information was lost.

A police sniper saw the moment Monis forced cafe manager Tori Johnson to kneel with his hands behind his head at 2:06am.

The sniper broadcast the information over his radio, but the inquest heard it was never received by officers in the Police Forward Command or the Police Operations Centre.

When Monis shot Mr Johnson at point blank range at 2:13am, the Tactical Commander initiated the call for an Emergency Action, but his radio failed.

It took a full minute for another officer to repeat the broadcast and for tactical police to breach the cafe's glass doors.

The inquest also heard the police negotiators only had one landline on which to make contact with the hostages, and many calls from the Lindt Cafe diverted to unmanned phones in the NSW Leagues Club, where the Police Forward Command centre had been set up.

The inquest also heard the negotiation team had been on duty since dawn, they were also responding to several other incidents across the state, and crucial information about Monis' demands was never passed on to them.

A team of negotiation experts from the United Kingdom told the inquest the NSW negotiators missed a number of opportunities to engage with the gunman.

It is likely Mr Barnes will take this evidence into account when he hands down his findings tomorrow.