Lindt Cafe siege remembered 10 years after terrifying images ...

On December 15, 2014, images from the heart of Sydney were being beamed live around the world into millions of homes.

And they were terrifying.

The tear-streaked faces of men and women being held hostage at gunpoint inside the Lindt Cafe, their hands pressed to the windows.

Petrified hostages running for their lives down Martin Place, into the arms of heavily armed tactical police.

And finally in the early hours of December 16, police storming to the cafe in a hail of gunfire, bringing the siege to its ultimate bloody end.

The images of hostages fleeing from the Lindt Cafe are seared in the minds of many. (AAP: Joel Carrett )

It is 10 years today since lone-wolf gunman Man Haron Monis walked into the Lindt Cafe and took 18 people hostage, demanding politicians declare Australia was under attack from Islamic State.

The Iranian-born radical self-styled sheikh was well-known to ASIO and police.

He'd been charged with plotting the murder of his ex-wife, as well as 43 sexual offences against women but was out on bail at the time.

Katrina Dawson and Tori Johnson's lives were taken. (AAP)

By the end of the 16-and-a-half-hour siege two hostages would be dead — cafe manager Tori Johnson was killed by Monis and barrister Katrina Dawson was fatally wounded by fragments of police bullets as officers opened fire on the gunman.

The failings of police commanders, intelligence agencies and the justice system would be put under the microscope in a marathon coronial inquest.

In the wake of the siege, NSW Police changed their strategy for dealing with terrorist situations, adopting a shoot-now approach instead of the previous contain and negotiate procedure.

But for the hostages who survived and the first responders who rushed to the scene, the scars from that day will last a lifetime.

Ben Besant took down terrorist Man Haron Monis during the siege at the Lindt Cafe. (ABC News: Andrew Whitington)

For most of the last decade, former Tactical Operations Unit officer Ben Besant was unable to be identified as the man who shot Monis dead and instead could only be referred to as "Officer A".

The coroner had placed a suppression order on his name, but that was lifted two weeks ago after Mr Besant won a court battle to reclaim his identity.

Petrified hostages ran for their lives. (AP: Rob Griffith)

After the siege he remained in the Tactical Operations Unit for another six years, despite suffering from crippling PTSD.

"I knew that Lindt had really impacted on me and I had to fight to really lock it away," he said.

"I ticked all the boxes in relation to PTSD.

"The hyper vigilance, I was always ready for the next gunfight … there was pretty much no sleep for years and if I did sleep I had really bad nightmares so I didn't want to sleep."

The siege left a lasting emotional impact on first responders and survivors. (AP: Rob Griffith)

Mr Besant had also held Katrina Dawson in his arms as she took her last breaths on the floor of the Lindt Cafe.

"She just looked at me and we sort of looked into each other's eyes and I could tell she was not in a good way," he said.

He was devastated to later learn it was fragments of police bullets that had killed her.

"Anytime I saw a blonde woman I'd instantly believe it was Katrina Dawson and go into panic attacks," he said.

"I just completely believed that it was my fault and I always blamed myself. That was the one moment that I couldn't process and I couldn't lock away and couldn't deal with. It's a moment I relive every night."

Mr Besant says there was every reason to believe at the time that Monis was carrying a bomb. (ABC News: Andrew Whitington)

While police commanders were widely criticised for their handling of the siege, Mr Besant said there was every reason to believe at the time that Monis was carrying a bomb in his backpack, which had wires protruding from it.

"I can defend the bosses decisions up until a point," he said.

"I believed it was a bomb, they believed it was a bomb, all the intelligence told us that it was a bomb. So if we made entry and the terrorist decided to detonate it would have killed everyone inside the cafe.

"So I can understand why they didn't send us in. But I'll say that up to a point — the point when he fired on the hostages running out the other foyer. From that moment I can't really defend or agree with their decisions."

However, Mr Besant felt police were not always given a fair run in the wall-to-wall media coverage during the coronial inquest into the siege.

"It was very difficult, there was a lot of police-bashing."

The siege ended in a bloody gunfight. (ABC News: Greg Hatch)

Eventually after intensive exposure therapy and a range of other measures, Mr Besant started dealing with his trauma.

"I just adopted the fact that I did have PTSD and that was my new threat, just like the terrorist at Lindt was a threat, and I needed to confront it."

Mr Besant said one of the reasons he wrote his book, Tiger Tiger Tiger, about the siege was to help others suffering PTSD and he is now relieved he can use his own name.

"You can't beat PTSD alone, I've tried it for years and failed miserably. You have to fight it, you can't shy away from it or it just gets worse."

Mr Besant said he would spend at least part of the siege anniversary with survivor Louisa Hope, who spent three months in hospital recovering from the injuries she received that day.

Louisa Hope was chosen by the gunman as a human shield and sustained a bullet wound to the foot. (ABC News: Timothy Ailwood)

During the siege Monis repeatedly used Ms Hope, who has multiple sclerosis, as a human shield.

"Certainly through that day there were three particular times when I thought this is it, I'm going to die now. And it is still amazing to me, miraculous really, that I didn't die that day," Ms Hope said.

But despite it all she said she made a conscious decision not to hate the man who was terrorising her.

"Going through that day thinking I was going to die, I was determined I was not going to go to God with any kind of hardness of heart," she said.

"I thought well I'm not going to resent him, I'm not going to harbour any hate towards him — he's a fool."

Ms Hope said the siege had changed her life.

"A fellow hostage said to me, 'Louisa, first thing in the morning and last thing at night… I think about the siege, about that day'. And I find that too," she said.

"You know, it's always with you."

She said she believed police had learned lessons after the siege and the inquest that followed but there were still many unanswered questions.

"It was not just the police you know. We still haven't had answers to why Man Haron Monis was even on bail."

Troy Grant watched the incident begin to unfold from the window of his office. (ABC News: Chris Gillette)

Troy Grant was the NSW deputy premier at the time of the siege and watched it begin to unfold from the window of his high-rise office, just metres away.

"I just assumed at first it was an armed hold up," he said.

As events unfolded he headed to the crisis centre that had been set up to manage the siege and stayed at his post overnight, allowing then-premier Mike Baird to get some sleep.

"I'll never forget the phone call I had to make to wake him up and I handed the phone to Jeff Loy, the assistant commissioner at the time, who relayed the very tragic news."

Floral tributes filled Martin Place in Sydney in the wake of the siege. (ABC: John Donegan)

Mr Grant later became police minister and was tasked with overseeing many of the changes recommended in the wake of the siege.

He said many lessons were learned and he believes police are now better equipped to deal with any terrorist events in the future.

"I am confident, but there's never anything you can do with full assurance because every situation is different," he said.

Ten years on, the siege is still in the thoughts of Sydneysiders. (AAP: Dean Lewins)

Mr Grant said the siege "profoundly changed the city's innocence in a way", but the outpouring of love and grief and the sea of flowers that appeared in Martin Place in the days after proved that people would not be intimidated by would-be terrorists.

"They try to drive fear and division and more often than not what any terrorist act actually does is unite people … and I think that's what happened."