According to an Australian inquest, police should have ended the 2014 Sydney cafe siege as soon as the hostage-taker began shooting.

In December 2014, gunman Man Haron Monis held 18 people hostage inside the Lindt cafe until police stormed the building 17 hours later.

A coroner on Wednesday ruled it

The attack was a “terrorist incident” for which Man Haron Monis was solely responsible, a coroner said on May 24.

However, New South Wales Coroner Michael Barnes found authorities had made major errors, including by delaying entry, during which time a hostage was killed.

Cafe manager Tori Johnson was executed in the 10 minutes between Man Haron Monis firing his first shot and police storming the building, the coroner said.

Heavily armed officers shot Man Haron Monis dead, but stray police bullet fragments killed a second hostage, barrister Katrina Dawson.

New South Wales Police Commissioner Mick Fuller conceded police “should have gone in earlier”, in an interview released after the coroner’s findings.

Michael Barnes ruled police were ill-equipped to handle the siege, relied too heavily on a sole psychiatrist, and employed a “contain and negotiate” strategy which failed.

He also savaged an earlier decision allowing bail to Man Haron Monis, who had been charged with 43 assaults and being an accessory to his ex-wife’s murder.

Although Michael Barnes stressed the deaths were “not the fault of police”, he found failings with their actions, including:

• a 10-minute delay between Man Haron Monis firing his first shot and police entering the building, allowing Tori Johnson to be “executed in the meantime”
• relying on “erroneous” advice from a psychiatrist who did not have sufficient terrorism expertise
• underestimating the gunman’s preparedness to kill or injure hostages
• allowing eight calls by hostages to police to go unanswered
• having some confusion around the lines of command.

Michael Barnes said a prosecutor had given inadequate information when Man Haron Monis faced an earlier bail hearing over his ex-wife’s murder.

“That [prosecution] solicitor erroneously advised the court that Monis did not have to show exceptional circumstances before he could be granted bail on the murder charges,” Michael Barnes said.

Man Haron Monis, an Iranian-born Australian citizen, had pledged allegiance to ISIS not long before the siege.

“It remains unclear whether Monis was motivated by Islamic State to prosecute its bloodthirsty agenda, or whether he used the organization’s reputation to bolster his impact in pursuit of his own ends,” Michael Barnes said.

On May 22, the families of Tori Johnson and Katrina Dawson criticized a police command tactic to intervene only if the gunman killed or injured someone.

“I’ll never be able understand how you can make a calculated decision that you wait for someone to die,” Tori Johnson’s mother, Rosie Connellan, told the Australian Broadcasting Corp (ABC).

In an ABC interview released on May 24, the police chief said it had been “wrong” to wait 10 minutes after Man Haron Monis first fired his shotgun.

After the findings, Tori Johnson’s partner, Thomas Zinn, said he still had respect for police despite the “failures of various authorities”.

“The pain deep in our hearts from losing Tori is as strong now as it was in December 2014,” he said.

“Everybody who knew Tori would agree that we lost a guardian angel that night.”

The state’s police union had criticized the inquest as a “witch hunt” that had scrutinized police officers “as if they were on trial”.

Michael Barnes acknowledged the police response carried extreme risk, and stressed his findings were specific to this incident.

His 45 recommendations included:

• police reassess their “contain and negotiate” strategy in possible terror scenarios
• developing a “cadre of anti-terrorist negotiators” with specialized expertise
• giving officers specific guidelines on assessing imminent risk
• creating a bail “mechanism” that authorities in all Australian jurisdictions could access
• more effective sharing of information between government agencies.