Sydney siege inquest told hostage Tori Johnson forced to kneel before being shot; Katrina Dawson hit by police bullet fragments

The inquest into last month's Sydney siege has heard chilling details of the final moments of hostages Katrina Dawson and Tori Johnson.

The first day of the inquest into the deaths of Mr Johnson, Ms Dawson and gunman Man Haron Monis heard Monis forced Mr Johnson to kneel before shooting him in the back of the head.

Counsel assisting the inquest, Jeremy Gormly SC, said as police moved in to end the 16-hour siege Ms Dawson was struck by six fragments of a police bullet or bullets, which ricocheted from hard surfaces into her body.

The inquest was told at least two police bullets or bullet fragments hit Monis in the head and 11 other bullets or fragments hit his body.

Mr Gormly said the siege at the Lindt cafe in Martin Place "seemed to break its way into the intimacy of Sydney life".

It ended when police stormed the cafe, shooting and killing Monis, after an officer witnessed him kill Mr Johnson.

"Mr Johnson was made by Mr Monis to kneel on the floor of the cafe," Mr Gormly said.

"After a short lapse of time Mr Monis simply shot him without further notice or warning in the back of the head."

The gun was about 75cm from Mr Johnson's head, and he probably died instantly, Mr Gormly said.

"The shot was witnessed by a police marksman who called it in," he said.

"That resulted in an immediate order to force entry of the cafe."

Fragments of police bullets injured three other hostages and one tactical response officer, who was struck in the face.

"They are all recovering," Mr Gormly said.

He said the investigation was "intensely detailed and broad" and would look at life of the gunman, the events during the siege, its termination and aftermath.

"The siege involved a large number of hostages - they are articulate, cooperative and demonstrate a good recollection of events," he told the inquest.

The court was told there was no CCTV inside the cafe but events were recorded from the outside.

Mr Gormly said if there were defects in the police force's management of the siege, "they will be exposed".

"This court has no difficulty making criticisms or adverse findings of police if it's necessary ... Every shot fired by Mr Monis and by police officers is likely to be accounted for."

A former member of the Australian military's elite domestic counter-terrorism unit has publicly suggested that police used the wrong rifles during the siege, with heavy bullets posing a high ricochet risk in the enclosed space.

Mitchell McAlister, writing in the American online journal SOFREP, a magazine presenting news and analysis from former special forces operatives, said he believed the choice of the M4A1 carbine may have contributed to the death of Ms Dawson.

'This is an attack. I have a bomb.'

The inquest heard Monis entered the Lindt cafe just after 8:30am, eating chocolate cake and drinking tea before moving to a rear table, where he had a fuller view of the cafe.

Mr Gormly said Monis then asked to speak to the cafe manager, Mr Johnson.

"Staff watching them knew Mr Johnson well and could tell from his body language that he was stressed by what he was hearing from the customer," Mr Gormly said.

"Mr Johnson then said to another employee, in a low voice, something like 'I need you to get my keys from the office and lock the doors. We're closed. Everything is OK. Tell the staff to be calm.'"

Mr Gormly said Monis then stood up, produced his gun and said: "This is an attack. I have a bomb."

After ordering the hostages to move to one section of the cafe and hold a flag to the window, Monis told Mr Johnson to call triple-0.

"Tori Johnson placed a triple-0 call and was told by Mr Monis what to say," Mr Gormly said.

"That was in effect that Australia is under attack by Islamic State and there are a number of radio controlled-bombs situated in Martin Place, Circular Quay and George Street.

"That proved to be false, ultimately."

Mr Gormly said Monis told the hostages he had a bomb in his backpack, which he did not take off during the siege.

"During the course of the siege, he said he would shoot people for various reasons - for example, that if he did so he would be taken seriously," Mr Gormly said.

Monis discharged five cartridges from his shortened pump-action shotgun during the siege.

The first hit an area above a door after hostages escaped, and the second killed Mr Johnson, Mr Gormly said.

The remaining shots fired by Monis were in response to police entering the cafe, but none struck any of the officers or hostages.

Monis was later found to have 21 more cartridges in his pockets.

The incident was treated as a possible terrorist attack, which "had a significant impact on the personnel and systems used to manage the siege", Mr Gormly said.

'Necessary to examine' why Monis was freed on bail

The inquest will also consider the fact Monis was on bail at the time of the siege, despite facing charges relating to his ex-wife's murder and numerous sexual offences.

"Bail operates contrary to the usual presumption of innocence and can result in someone being held in jail before their trial and when they are not yet found guilty," Mr Gormly said.

"Nevertheless bail is a system that in part aims to prevent offenders from offending again and to ensure they do not abscond before trial.

"Mr Monis was on trial at the time of the siege. It is necessary to examine without hindsight how he came to be granted bail."

The court was also told Monis had claimed that his actions were an attack by Islamic State (IS) but "seems he had not established contact with IS before siege".

The inquest will look into how cafe manager Mr Johnson, 34, and lawyer Ms Dawson, 38, died and whether their deaths could have been prevented.

State coroner Michael Barnes offered condolences to the family and friends of those who died in the siege.

"Rarely have such horrifying events ... unfolded so publicly," he said.

Mr Barnes said some questions might not be answered "because the only person who knew them is beyond reach".

Members of the Johnson family and hostage John O'Brien attended today's hearing.

Monis's partner Amirah Droudis was represented by lawyer Angelo Bilias.

The federal and state governments are jointly investigating how Monis was able to access a gun, what information security agencies had about him and why he was granted bail.

New South Wales Police is also conducting a critical investigation into officers' actions during the siege.

Announcing the inquest last month, NSW Police Minister Stuart Ayres said it would help the public understand exactly what happened.

"It will allow us to get better at what we do," he said.

Mr Johnson was one of several Lindt cafe workers taken hostage by Monis.

He had worked there since October 2012 and was previously employed at a string of other restaurants and hospitality companies in Sydney.

Ms Dawson was having coffee with a pregnant friend in the cafe when they were taken hostage.

The hearing has been adjourned to a date to be announced before the end of March.