Forensic services work investigate the scene of the 17-hour standoff at the Lindt Chocolat Cafe. Picture: Bill Hearne Source: News Corp Australia

A crime reconstruction will form a crucial part of the police investigation as detectives seek to answer questions over what really happened at the Lindt Chocolate Cafe siege, especially the final moments.

Armed with information from police accounts, CCTV footage, photographs and physical evidence examined with the crime scene still in place, police are expected to do a chronological “walk-through” of the area, and reconstruct some of the crucial moments of the siege that gripped Sydney.

Forensic officers begin their investigation. Pics Bill Hearne Source: News Corp Australia

It sounds like CSI stuff, but crime reconstructions are often carried out in serious criminal investigations, according to forensic criminologist Dr Claire Ferguson, an expert in crime scene studies at the University of New England.

“Crime reconstruction is an important part of a criminal investigation. It’s not that common, but this is obviously a very important investigation for the police department and for all the agencies involved,” Dr Ferguson told news.com.au.

“Basically what they’re trying to do is retrace as best as possible what happened by going through milestone moments throughout the ordeal. They’ll know the locations of certain people at certain times, where shots were fired from.”

NSW Police Commissioner Andrew Scipione has advised investigations are well underway. Picture: Mark Metcalfe. Source: Getty Images

Forensic criminologist Dr Claire Ferguson explains how an investigation of this scale could go down. Source: NewsComAu

The Sydney siege investigation is unique, Dr Ferguson explained, because it would not go to court. There’s no one to prosecute. Rather than collecting evidence to present as part of a criminal case, police and other agencies involved will seek to discover exactly what happened in those 17 hours, and the days and week leading up them.

“It’s a massive undertaking for the police department and they’re not going to cut any corners,” Dr Ferguson said.

“This means reconstructing as much as they can of the actual physical crime scene. Going through what went on moment by moment and recording that in any way they can.

“Because this was a police operation, the findings of this investigation will also be used in any kind of civil case that could be brought forward — if family members, politicians, or any influential outspoken figures express some kind of concern about the way the situation was handled.”

Detectives from the homicide squad are leading the independent investigation with oversight from Professional Standards Command and the cafe site remains closed as investigators continue their work.

Ladders, cameras, and forensic technology have already been used in the investigation. Picture: Bill Hearne Source: News Corp Australia

The cafe remains a crime scene. Picture: Bill Hearne Source: News Corp Australia

Forensic investigations climbed ladders and set up special tents to gather evidence in the hours after the dramatic volley of gunfire brought the siege to an end.

The critical incident investigation, as NSW Police Commissioner Andrew Scipione has continuously advised, is well under way, but it will take months.

“We’ll get to the bottom of it, and the sooner the better,” the Commissioner said today.

Hundreds of hours of security footage from surrounding locations, and even vision tracking the movements of the hostage-taker will be analysed during the forensic investigation.

A senior police source told The Daily Telegraph the investigation “will look at every aspect of the incident”.

“They will be looking at how (gunman Man Horan) Monis got the gun, how he got to the cafe, what his motivation was,” the source said.

“Besides the interviewing of all those people directly involved, they will be trawling all social media sites Monis has viewed. They will look at his phone records, computers. Any data they can as well as interviewing his associates and even neighbours.”

The unprecedented investigation “will take some time”. Picture: Bill Hearne Source: News Corp Australia

Physical evidence continues to be gathered. Picture: Bill Hearne Source: News Corp Australia

Detectives will leave no stone unturned. Picture: Bill Hearne Source: News Corp Australia

Addressing the investigation, Commissioner Scipione said yesterday that about 70 interviews would be conducted.

Post mortem examinations, which have already been completed on the two innocent victims, Lindt cafe manager Tori Johnson, 34, and barrister and mother-of-three Katrina Dawson, 38. Their bodies will be released to their families tonight.

An autopsy is expected to be carried out on the 50-year-old gunman by the end of the week.

Weapons from officers involved in the forced entry into the cafe have now been handed in to the NSW Ballistics unit, as has the shotgun used by Monis.

Physical evidence, bullets, shells, anything left behind in the horrific crime scene left after police stormed the cafe, shooting through windows with several rounds before bringing the siege to an end, will be examined.

Once the police investigation is complete, a brief of evidence will be provided to the State Coroner for an inquest to be conducted “as soon as is reasonably practicable”.

“Their work has really only just started. It’s going to take a long time,” Dr Ferguson said.

“But that’s what needs to be done to find those answers.”

Floral tributes surround the crime scene at Martin Place. Picture: Bill Hearne Source: News Corp Australia