Michael O'Connell, SC, put it to the officer on Wednesday that he had changed his story about whether he fired his gun, where and how.

"The reason why you've changed your account in the ways which we've just gone through is because the account you've provided has not been truthful," Mr O'Connell said.

Officer B, whose name has been suppressed, told a coroner he was telling the truth. He said the trauma of the operation and a shrapnel wound had affected his memory.

Ms Dawson was struck and killed by seven police bullet fragments after assault teams entered the stronghold and shot dead the gunman, Man Haron Monis.

Ballistics analysis cannot trace the fragments back to any of the five rounds Officer B fired or the 17 fired by his colleague, Officer A.

The night of December 16, 2014, was a "surreal experience", Officer B has said several times.

Another officer recorded him saying a few hours after the siege that he did not fire his gun. During an interview three days later, he said he did not know.

He told the inquest that, three weeks after the interview, three or four seconds of memory came back and he clearly recalled firing a single burst of bullets at Monis.

But Mr O'Connell said this was not what Officer B told his lawyer in March.

"You instructed your solicitor that you had no recollection of whether you had discharged all five rounds from your rifle in one burst," he said.

Mr O'Connell put it to Officer B that he fired after he had been hit in the face by shrapnel and Monis was already dead on the ground.

Officer B, at the invitation of a police barrister, repeated to coroner Michael Barnes the version of events he gave the day before. He said he saw Monis, fired, felt a burning in his face, fell over and did not fire again.

On Wednesday morning, the family for killed cafe manager Tori Johnson objected to the "sorrow" Police Commissioner Andrew Scipione expressed in a formal statement to the inquest.

Gabrielle Bashir, SC, for the Johnson family, asked for the sentence to be struck out.

Ian Freckelton, QC, for the police, said it communicated Mr Scipione's "deep sorrow and regret" about the lives lost in the siege.

"The commissioner did want to express that he is sensitive to the tragic loss that has been suffered by the families," he said.

Ms Bashir responded: "Dr Freckelton has put that on the record against the express wishes of Tori Johnson's family."

The coroner ruled the whole statement admissible, saying it broke no rules of evidence and the family could respond in closing submissions.

Last week, Mr Johnson's mother, Rosie Connellan, yelled at a police forward commander, calling him an "absolute disgrace" as she left the inquest abruptly.

The police forward commander had referred to the operation to end the siege as "high-stakes games" and declined to apologise. He also said Monis had had "the same rights as everyone else".

Mr Scipione could be called as a witness as early as next week.