The final, brutal moments of the Sydney siege have been officially revealed and will bring little comfort to the grieving families of the slain victims.

At the first day of an inquest into the Lindt Chocolate Cafe hostage drama, counsel assisting the inquiry said barrister and mother-of-three Katrina Dawson was killed after being hit by six fragments of a police bullet which ricocheted into her body.

The court also heard on Thursday that cafe manager Tori Johnson was told to kneel on the floor of the cafe before being executed by a gunshot into the back of the head, without warning, by gunman Man Haron Monis.

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It was these gunshots which triggered the swift and deadly police response. Heavily armed officers stormed the Martin Place cafe just seconds after Mr Johnson was shot, killing Monis while he attempted to reload his shotgun, but also mortally wounding Ms Dawson.

Monis was struck twice in the head by fragments of police bullets, and 11 times in the body.

The court heard that fragments of police bullets also injured three other hostages and one tactical response officer, who was struck in the face.

“They are all recovering,” said counsel assisting the Coroner, Jeremy Gormly SC.

Floral tributes for victims of the Lindt Cafe siege fill Martin Place in Sydney, close to where the siege took place. Photo: Getty

Mr Gormly said Monis held the gun about 75cm from Mr Johnson’s head, and he probably died instantly.

“The shot was witnessed by a police marksman who called it in,” Mr Gormly said.

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

While some doubts may always remain as to what drove Monis to carry out the attack, the inquest hopes to explain virtually everything else that happened that day.

No witnesses were called on the opening day, but counsel assisting outlined the scope of the inquest and the results of inquiries made to date.

As he opened proceedings, NSW Coroner Michael Barnes said “such horrifying events have rarely unfolded so publicly”.

“The protracted nature of the siege; its morbid suspense and the explosive climax must have made manifold the grief of the families of the hostages who died.”

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.

Members of the Johnson family and hostage John O’Brien attended Thursday’s hearing.

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Inside the mind of Monis

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.

Gunman Man Haron Monis killed during the siege at the Lindt Chocolate Cafe in Sydney’s Martin Place was an Iranian cleric with a violent criminal past. Photo: Getty

“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.”

When police stormed the cafe, 16 hours later, two police bullet fragments hit Monis in the head, with 11 others peppering his body.

It seems Monis was trying to re-engage another round when he died, the inquest was told.

Monis’ psychiatric profile, his associations and political and religious activity, as well as his relationships, will all be examined.

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

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.

Sydney siege hostage John O’Brien addresses the media at the NSW Coronial Inquest. Photo: AAP

TV hostage interviews won’t affect inquest

Sydney cafe siege hostages who sold their stories to TV networks for large sums of money have the right to do so, the inquest was told.

“At present, however, the law is that unless there is a contempt it’s not automatically illegal for a witness to give a paid interview,” Mr Gormly said.

Survivor Marcia Mikhael has been signed by the Seven Network, and was reportedly paid more than $300,000, while 82-year-old hostage survivor Mr O’Brien was reportedly paid $100,000.

A further six survivors have been secured by Nine, which is understood to have paid $1 million for the combined package.

The inquest was adjourned with a future hearing date and location yet to be set.