Police feared a customer inside the Lindt Cafe was aiding and abetting gunman Man Haron Monis, an inquest into the Sydney siege has heard.

NSW Assistant Police Commissioner Mark Murdoch said they reached out to various contacts in the community to get information about Monis not long after he took 18 hostages on December 15, 2014.

Assistant Commissioner Murdoch, who is head of a police counter-terrorism unit, said they tried to identify who they were dealing with as quickly as possible during the siege.

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“It’s a big animal and there are many moving parts … it’s my job to co-ordinate those moving parts,” he said.

“In the space of 15-20 minutes we had information come from about four separate sources.”

The witness said at first they suspected a “sleeper” was inside the cafe with Monis and they feared that person was a customer.

Counsel Assisting Jeremy Gormly SC asked: “Knowledge about Monis was always going to be helpful to negotiators?”

Assistant Commissioner Murdoch replied: “Yes.”

‘It was my objective to make direct contact with Monis’

He agreed that information about Monis on police charge sheets for his previous crimes would have been helpful to police negotiators.

The Assistant Commissioner said he was not aware of any reason, such a privacy issues, that any information was withheld.

He said it was not ideal to be communicating with the gunman through hostages and he would have “felt more comfortable” with direct contact.

Monis died in the siege. Photo: AAP

“It was my objective to make direct contact with Monis,” Assistant Commissioner told the inquest.

“At the end of the day we were there to secure the safe release of the hostages.”

He said there was talk with police negotiators about sending text messages to the gunman but there were, to his knowledge, no plans to turn off water and power to try to drive him out of the cafe.

Mr Murdoch said the “contain and negotiate”‘ approach police took during the siege was a worldwide practice adopted around the 1990s, but it was now being revised in Australia and overseas following recent incidents involving “active shooters”.

He said it followed several incidents in which police fatally shot people after forcing entry into buildings.

The inquest heard one such incident was the fatal police raid on the Sydney home of 29-year-old Aboriginal man David Grundy in 1989.

Mr Murdoch said there is a significant risk for police first responders in an “active shooter” environment and officers needed to be able to deal with that risk.

Fears of more loss of life if police stormed cafe

Assistant Commissioner Murdoch said during the siege they knew Monis was armed and they thought he had a bomb, and did not know how or when he would detonate it.

He said if they had forced their way into the cafe they feared Monis would have time to start shooting hostages and explode the bomb.

Police stormed the cafe after 17 hours. Photo: AAP

“They’re big considerations we needed to balance,” the Assistant Commissioner said.

“It wasn’t as simple as saying – he’s pointing a gun, let’s get in there. Whilst two innocent young Australians lost their lives … it could have been a whole lot worse.”

Mr Murdoch was questioned about why police snipers positioned outside the cafe did not shoot at Monis earlier.

He said the snipers could not be sure of killing him and must apply certain criteria before shooting at offenders.

Mr Murdoch said police were trained not to shoot an offender unless there was a prospect of death or injury to others.

He said that was not the case when he was in charge of the siege from midday until around 9:30pm.

Mr Murdoch said snipers were trained to act with caution and may have faced criminal prosecution if they had tried to shoot Monis before he killed cafe manager Tori Johnson.

After waiting 17 hours, police stormed the cafe when Monis fatally shot Mr Johnson in the back of the head.

Officers then shot Monis dead and hostage Katrina Dawson died after being hit by police shrapnel.

The inquest continues before coroner Michael Barnes.

-ABC