The inquest into the Martin Place siege will have an unprecedented focus on social media as investigators trawl through thousands of sources documenting one of Sydney's most public crimes.

A team of more than 30 police detectives and experts have been reviewing evidence since the siege's violent end on December 16 that left two hostages and the gunman dead.

At the opening of the coronial inquest on Thursday, counsel assisting the Coroner, Jeremy Gormly, SC, said the 17-hour ordeal had been captured in "hundreds of hours of material".

The inquest will seek to provide answers to issues such as how Man Haron Monis obtained a shotgun, his motivations, associations and actions in the lead up and during the siege at the Lindt Cafe.

But unlike most inquests, this one will also explore the role of social media communications, which police believe played a significant enough role to merit the focus.

"What interactions occurred between hostages, police, non-police parties and hostage families? How did social media contact impact the prospects of the resolution?" Mr Gormly asked.

The hostages used social media to contact family members and friends but also to communicate the demands of Mr Monis.

One such post was uploaded to Facebook during the siege by Westpac employee Marcia Mikhael, who wrote on her page she was being held hostage by a member of IS.

"The man who is keeping us hostage has asked for small and simple requests and none have been met. He is now threatening to start killing us. We need help right now."

During the siege NSW Deputy Police Commissioner Catherine Burn confirmed they were following conversations on Twitter to inform their tactical response as well as monitoring Facebook posts by the 18 men and women trapped inside the cafe.

Investigators will continue to analyse Facebook page updates, emails, videos posted to social media sites and "other social media exchanges".

There is also ample footage and audio materials captured by media groups and CCTV footage captured by neighbouring cameras.

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As the event was so widely and intensively covered, Mr Gormly said they were likely to finish the inquest with a very high level of detail and understanding.

"We will most likely have a detailed and comprehensive picture of virtually every aspect of the siege, its cause, its lead up, the detail of the life of Mr Monis, the events during the siege, its termination and its aftermath."