One of the hostages who died during a siege at a Sydney cafe was killed by fragments of a police bullet, an inquest has heard.

Katrina Dawson, a 38-year-old barrister, was struck by six fragments of a police bullet which ricocheted off the walls when officers stormed the building to end the 16-hour siege.

"One fragment struck a major blood vessel. She lost consciousness quickly and died shortly afterwards," said Jeremy Gormly, one of the lawyers assisting the coroner.

The second hostage who died - cafe manager Tori Johnson - was killed by Iranian-born gunman Man Haron Monis, moments after several people managed to flee the coffee shop safely.

Mr Gormly added: "Mr Johnson was made by Monis to kneel on the floor of the cafe. After a short lapse of time, Monis simply shot him without further notice or warning in the back of the head.

"The end of the barrel was about 75cm from his head at the moment of discharge. Mr Johnson is believed to have died immediately."

It was the 34-year-old's death which led tactical operatives to force their way into the Lindt cafe in the early hours of December 16.

Trained officers threw 11 flash bangs into the building before they fired 22 shots at Monis.

"At least two bullets, police bullets or bullet fragments hit Monis in the head and 11 other bullets, police bullets or fragments hit him in the body. It seems he was killed instantly," Mr Gormly told Glebe Coroner's Court.

Gunman

The inquest also heard of the gunman's movements early on in the day's events - how he first ordered and ate a piece of chocolate cake and drank tea after entering the cafe on the morning 15 December.

Around half an hour later, he asked to move tables and to speak to manager Johnson, who then asked an employee to lock the doors.

Monis then stood up, putting on a vest and bandana, and told staff: "This is an attack. I have a bomb."

The inquest aims to determine what happened during the siege, and investigate whether emergency services' response to the hostage situation was sufficient.

It will also examine the motivations of Man Haron Monis.

Although the gunman claimed his attack was in affiliation with Islamic State, it has emerged that he had no contact with the terror organisation before the siege.

Mr Gormly said there was evidence that a psychiatric profile of Monis "will throw light" on his motivations, he said.

Originally posted at 7.16am