A bullet fired by Australian police killed one of 18 hostages held at a café by an Islamist extremist last month, an inquiry into the siege has found. 

Speaking at a Thursday judicial inquiry held at a coroner's court in New South Wales, officials said Katrina Dawson was killed by bullets or fragments of bullets fired by police during their raid on the Lindt chocolate cafe in Sydney on Dec. 15, the BBC reported. 

The 38-year-old mother of three was "struck by six fragments of a police bullet or bullets which ricocheted from hard surfaces into her body," said Jeremy Gormly, an attorney who is helping the New South Wales coroner. 

"I will not detail the damage done to Ms. Dawson other than to say that one fragment struck a major blood vessel. She lost consciousness quickly and died shortly afterwards."

The inquest also learned that the gunman, Man Haron Monis, forced another hostage, cafe manager Tori Johnson, to his knees before shooting him in the back of the head, The Sydney Morning Herald reported. 

It was Johnson who called police after Monis, and Iranian refugee with Australian citizenship, held customers at the cafe hostage with a firearm he concealed inside a blue plastic bag. 

"Australia is under attack by Islamic State and there are a number of radio controlled bombs in Martin Place, Circular Quay and George Street," Johnson told the dispatcher from triple-0 at around 9:44 a.m. local time, according to The Sydney Morning Herald.

Monis, who has a history of religious extremism, ordered the hostages to display an Islamic flag in the window. 

The siege ended 16 hours later with Monis being killed by two police snipers who stormed the cafe and open fired, sticking the gunman with 11 bullets, the inquiry leaned. 

The hearing, attended by some of the survivors, is to determine if any of the deaths resulting from the siege could have been prevented, the BBC reported. 

The investigation is ongoing.