Gunman Man Haron Monis forced Lindt cafe manager Tori Johnson to kneel before shooting him once in the back of the head, an inquest has heard.

Counsel assisting the coroner, Jeremy Gormly, SC, has also revealed barrister Katrina Dawson was struck by six fragments of police bullets after they ricocheted off hard surfaces inside the cafe, with one striking a major blood vessel.

The 38-year-old mother of three lost consciousness and died shortly afterwards.

The revelations came as an inquest into the deadly Martin Place siege opened at the Coroner's Court in Glebe on Thursday.

The inquest was attended by hostage John O'Brien, 82, and six family and friends of Mr Johnson. The Dawson family did not attend.

Details of the final moments of the 17-hour ordeal emerged for the first time, including the execution-style killing of Mr Johnson which forced police to storm the cafe.

Monis had told the hostages he had a bomb in his backpack and would shoot people for various reasons, including to ensure he was taken seriously, the inquest heard.

When several hostages escaped, he became enraged. He fired the first of five shots at hostages who escaped several hours before the siege came to its deadly climax, the inquest heard.

The second time he discharged his gun was at 2.14am when, without warning or notice, he killed Mr Johnson.

A sniper witnessed the shot and police immediately forced entry into the cafe using specially designed bullets to smash open the glass doors and windows.

The heavily armed officers threw 11 SF9s "flash bangs", which set off 99 loud bangs and flashes of light mimicking a hail of bullets.

Two marksmen, identified only as entry officers A and B, fired 22 rounds at Monis, who discharged two shots in return.

Monis was killed instantly after two bullet fragments entered his head and 11 others lodged in his body.

It appeared he was trying to reload his firearm when he was killed, the inquest heard.

The marksmen were represented by solicitors at the inquest on Thursday and successfully applied to have their identities kept secret.

Counsel assisting the coroner, Jeremy Gormly, SC, said the inquest would examine the management of the siege among many other aspects.

He said more than 30 detectives plus officers and experts were working on the case. There would be no hesitation in making adverse findings or criticisms against the police if necessary.

- with Rose Powell