The fourth and final stage of the Sydney siege inquest began this week.

It's heard evidence from some of the 17 hostages held at gunpoint in the Lindt Cafe for up to 16 hours in December 2014.

It included video and audio never before released to the public.

Hack has pieced together the witness evidence so far to reconstruct the events of the siege.

We've also spoken with Chris Reason - the only journalist allowed to watch the siege from inside Channel 7's Martin Place studios. He's been reporting on the inquest since it began in May 2015.

The inquest will continue for several months and the coroner will deliver his report later this year.

What do we know now, and what questions have not yet been answered?

Accomplice at large?

About 9:20am on Monday, December 15, barrister Michael Klooster went into the Lindt Cafe in Sydney's Martin Place. He was there to grab a quick coffee before court. Somebody called his name, he turned and saw it was a former client, Man Haron Monis.

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Whatsapp Man Haron Monis in 2009.

Monis and the barrister spoke for a few minutes, Klooster told the inquest on Wednesday.

"It was like talking to someone at a bus stop," he said

"For someone who was about to do what he did he was very cool, calm and collected."

Klooster did not know that inside Monis' black backpack was a speaker with wires, a pairing knife, a sawn-off pump-action shotgun, a mobile phone, ammunition and other items.

Monis had walked to the cafe through the morning rush hour.

CCTV footage played at the inquest showed Monis wearing the backpack and making his way on foot through Sydney CBD to the Lindt Cafe from about 8:30am.

But how he got to the Sydney CBD is not known.

The inquest was shown no CCTV evidence Monis took a bus, train or taxi from his unit in Wiley Park, which is about a 45-minute bus ride from the cafe.

"Police have gone to hotels and checked all of them," Chris Reason told Hack. "They've seen if he stayed in the city overnight."

"The conclusion at this stage is someone assisted, someone drove him in and dropped him off.

"And therefore there could be an accomplice at large."

The siege begins

In the Lindt Cafe, Monis asked Klooster if he wanted to have a coffee to discuss appeal avenues, the barrister told the inquest.

Klooster declined and left.

A short time later care worker Rosemary Birt tried to enter the cafe, but it appeared to be locked. She signalled to people inside and they avoided eye contact and gestured for her to go away.

A waitress held up a handwritten note saying "closed".

Rosemary told the inquest she then saw through the cafe windows a man in a baseball cap stand up and pull a sawn-off shotgun out of a plastic bag.

Backing away she fumbled typing the pin into her phone to call police.

Inside the cafe, Monis ordered cafe manager Tori Johnson to call triple-0 and read a message to the operator that said Australia was "under attack by Islamic State".

A recording of the call was played to the inquest on Monday.

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Monis would shoot Tori in the back of the head about 17 hours later, in the final moments of the siege.

Part of the message read:

"The plan is to request Tony Abbott to call them or me and to have them have a debate, while it is broadcast live on ABC national radio."

Tori told the operator what Monis had told him: bombs had been placed at three locations in Sydney's CBD.

"There is a bomb here," Monis told the hostages.

His backpack looked like it might have a bomb - Monis had put an ordinary speaker inside so that the wires poked out.

This created "the illusion of him carrying a bomb," the counsel assisting told the inquest.

Even as police were responding to the first triple-0 calls, Monis ordered the hostages to stand against the cafe's windows.

The Lindt Cafe is opposite Channel 7's Sydney headquarters - soon images were being broadcast of the pale hands of hostages pressed against the glass.

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Whatsapp Hostages in the Lindt Cafe.

The siege had begun.

Should police have moved earlier?

Police arrived within moments of the first triple-0 call, the inquest heard.

Barrister Michael Klooster, who was working on the eight floor of the Lindt Cafe building, saw the media reports and phoned the Federal Police. He told them he had seen Monis in the cafe earlier.

By 11:00am the situation was declared an act of terrorism.

Police command points were set up and snipers took vantage points around the cafe.

An internal police debate began about whether to raid the premises or follow the established protocols and wait until a hostage had been injured or killed.

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Whatsapp Katrina Dawson and Tori Johnson were killed in the final moments of the siege.

"The head of the Tactical Operations Unit had been arguing at least earlier in the day that they could breach the building earlier," Chris says.

"They decided to not do it - they decided to go with the protocol.

"And now that is a serious question."

An independent UK police inquiry into the operation of NSW police that night recommended police should have broken the siege earlier.

But the inquiry also found NSW police had mostly done the right thing. The inquest was told the UK inquiry found the outcome of the siege wouldn't have been much different if the military had been used, instead of police.

"I know people in the Army would dispute that," Chris Reason told Hack.

"It’ll be interesting to see what evidence they'll present to support that situation."

The 16th hour

After 16 hours under siege, Monis' behaviour had become erratic. Police had rejected his attempt to exchange hostages for an Islamic State flag. Media organisations were also refusing to broadcast his message the siege was an attack on Australia by Islamic State.

Night had fallen, and powerful lights were being shone through the windows of the cafe.

Monis would have guessed snipers were watching him.

"It's really interesting to look inside the cafe at that time," says Chris Reason, who was crouched on the fourth floor of the Channel 7 studios building, beside a television cameraman and two police snipers.

"It's been going for 16 hours and Monis is agitated, swinging between states of absolute paranoia.

"He's forcing hostages to stack boxes and chairs in front of the doors. He's worried about a potential police raid."

Monis ordered a hostage, Selina Win Pe, a Westpac manager, to phone police and beg them to extinguish the lights shining into the cafe. She told police she would be shot if they did not.

Her phone call was played to the inquest:

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"There in the voice of Selina Win Pei we really get a sense of how terrifying it must have been," Chris says.

"She's pleading with the police officer for the duration of that call begging him to extinguish the lamps at the insistence of Monis.

"Monis is terrified the lights are shining inside and giving police an advantage on where he's located inside the cafe."

Police refused to switch off the lights.

'Window two, hostage down'

Shortly after 2:00am - in the final hour of the siege - a group of hostages fled the cafe.

CCTV footage played at the inquest on Tuesday shows the hostages running and then smoke and debris from Monis' shotgun blast.

The video footage suggests Monis was trying to shoot the escaping hostages, and not firing a warning shot, the counsel assisting the coroner told the inquest.

Minutes later he ordered cafe manager Tori Johnson to put his hands behind his head and kneel.

He told the other hostages everything would be OK.

On the fourth floor of the Channel 7 studios building, the sniper beside Chris Reason watched Monis shoot Tori in the back of the head.

"Window two, hostage down," the sniper reported.

The Tactical Operations Unit threw 'flashbang' devices through the cafe's main doors to stun and disorient Monis, and then two officers with authority to shoot to kill went in through the front doors.

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The inquest identified them as officers A and B. They shot 17 and five founds respectively.

"Once they were sure Monis was down and dead they checked him for signs of life," Chris says.

"They went quickly through the cafe to look for other hostages. One saw Katrina still moving under a table.

"She was struggling to breathe. There was a pool of blood under her."

Paramedics rushed Katrina to hospital but in the small hours of Tuesday morning the 38-year-old lawyer was declared dead.

The inquest confirmed a police bullet had killed her.

Across town, at the Supreme Court, her family was waiting with the families of the other hostages. As the survivors were reunited with loved ones, the number of remaining families whittled down.

"By the end of morning there were only two families left," Chris says.

"The Johnson family and the Dawson family complained they effectively worked out their loved ones had died through a process of elimination.

"That was a quite confronting moment in the court room."

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Whatsapp Katrina Dawson's parents, Jane and Alexander Dawson, arrive at the inquest.

Editors note: an earlier version of this article referred to Katrina Dawson as being 34 years old, she was 38.